Mesozoic Sentence Examples
Not improbably this country was either "Gondwana-land," connecting Mesozoic India with Africa, or perhaps Africa itself.
In the western region all the Mesozoic systems, including the Trias, are well developed.
The Mesozoic begins with a Triassic land period in the mainland of Australia; while the islands of the Australasian festoon contain the Triassic marine limestones, which fringe the whole of the Pacific. The Triassic beds are best known in New South Wales, where round Sydney they include a series of sandstones and shales.
And when we know that the Chrysomelidae and Buprestidae also lived in Triassic, and the Carabidae, Elateridae, Cerambycidae and Scarabaeidae, in Liassic times, we cannot doubt that the great majority of our existing families had already been differentiated at the beginning of the Mesozoic epoch.
The Mesozoic system is not well developed.Advertisement
The Mesozoic beds are limited in extent, the most extensive areas lying around the Gulf of Orosei on the east and west of Sassari in the north.
As far west, therefore, as the Cordillera, there is no evidence that any part of the region was ever beneath the sea in Mesozoic times, and the plant-remains indicate a land connexion with Africa.
Within the northern circle of the 8 lie the Mesozoic and Tertiary beds of the Paris basin, dipping inwards; within the southern circle lie the ancient rocks of the Central Plateau, from which the later beds dip outwards.
In France, as in Great Britain, volcanic eruptions occurred during several of the Palaeozoic periods, but during the Mesozoic era the // /
Under the heading of Multituberculata will be found a brief account of certain extinct mammals from the Mesozoic formations of Europe and North America which have been regarded as more or less nearly related to the monotremes.Advertisement
Neumayr, while they regard the basin of the Pacific as of great antiquity, believe the Atlantic to date only from the Mesozoic age.
Both were in turn replaced by the Lower Mesozoic flora, which again is thought to have had its birth in the hypothetical Gondwana land, and in which Gymnosperms played the leading part formerly taken by vascular Cryptogams. The abundance of Cycadean plants is one of its most striking features.
Though now on the way to extinction, Cycadeae are still widely represented in the southern hemisphere by genera which, however, have no counterpart in the Mesozoic era.
Over the greater part of the Cambrian country the strata are still nearly as flat as when they were first laid down, and the deposits, even of the Cambrian period, are as soft as those of the Mesozoic and Tertiary formations in England.
At the beginning of the Mesozoic era the whole country became land, bearing upon its surface the salt lakes in which the Trias was laid down.Advertisement
E Arabian Sea Ba Of G A L e Geological information incomplete Desert Deposits Quaternary Tertiary Mesozoic Palaeozoic Archaean and Metamorphic Younger Volcanic Rocks English Miles b iuHi iiiiuiiiiii after llargl,aua Geology The geology of Asia is so complex and over wide areas so little known that it is difficult to give a connected account of either the structure or the development of the continent, and only the broader features can be dealt with here.
In the south, in Syria, Arabia and the peninsula of India, none but the oldest rocks are folded, and the Upper Palaeozoic, the Mesozoic and the Tertiary beds lie almost horizontally upon them.
North of this lies a broad belt in which the Mesozoic deposits and even the lower divisions of the Tertiary system are thrown into folds which extend in a series of arcs from west to east and now form the principal mountain ranges of central Asia.
North of the folded belt, and including Emery the greater part of Siberia, Mongolia and northern China, lies another area which is, in general, free from any important folding of Mesozoic or Tertiary age.
In the extreme north, in the Verkhoyansk range and in the mountains of the Taimyr peninsula, there are indications of another zone of folding of Mesozoic or later date, but our information concerning these ranges is very scanty.Advertisement
It is interesting to observe, as will be shown later, that during the Mesozoic era there was a land-mass in the north of Asia and another in the south, and between them lay the sea in which ordinary marine sediments were deposited.
Between these ancient land masses lies an area in which marine deposits of Mesozoic age are well developed and which was evidently beneath the sea during the greater part of the Mesozoic era.
Here again there are no marine beds of Mesozoic or Tertiary age, while plant-bearing deposits belonging to the Angara series are known.
Southern China is very different in structure, consisting largely of folded mountain chains, but the geological succession is very similar, and excepting near the Tibetan and Burmese borders, there are no marine deposits of Mesozoic or Tertiary age.
The Triassic deposits of the Verkhoyansk Range show that this land did not extend to the Bering Sea; while the marine Mesozoic deposits of Japan on the east, the western Tian-shan on the west and Tibet on the south give us some idea of its limits in other directions.Advertisement
Marine Tertiary beds occur in Burma; in the Himalayas and in south Tibet there is a nearly complete series of marine deposits from the Carboniferous to the Eocene; in Afghanistan the Mesozoic beds are in part marine and in part fluviatile.
The Silurian mica-schists of Bergen in Norway are fossiliferous; in the Alps it is believed that even Mesozoic rocks pass laterally into mica-schists and talc-schists.
With the dawn of the Mesozoic epoch we reach Hexapods that can be unhesitatingly referred to existing orders.
None of the groups of existing Endopterygota have been traced with certainty farther back than the Mesozoic epoch, and all the numerous Palaeozoic insect-fossils seem to belong to forms that possessed only imperfect metamorphosis.
As shown by the number and variety of species, the Orthoptera are the most dominant order of this group. Eminently terrestrial in habit, the differentiation of their fore-wings and hindwings can be traced from Carboniferous, isopteroid ancestors through intermediate Mesozoic forms. The Plecoptera resemble the Ephemeroptera and Odonata in the aquatic habits of their larvae, and by the occasional presence of tufted thoracic gills in the imago exhibit an aquatic character unknown in any other winged insects.
The occurrence of weevils - among the most specialized of the Coleoptera - in Triassic rocks shows us that this great order of metabolous insects had become differentiated into its leading families at the dawn of the Mesozoic era, and that we must go far back into the Palaeozoic for the origin of the Endopterygota.
The only Mesozoic system which is represented in Brazil by marine beds is the Cretaceous, and the marine facies, is restricted to the coasts and the basin of the Amazon.
The hilly regions of Transylvania and of the northern part of Hungary consist of Palaeozoic and Mesozoic rocks and are closely connected, both in structure and origin, with the Carpathian chain.
The second element in the composition of the island consists of Mesozoic beds, which occur in a broken band along most of the south-western coast.
Geology.'--The Eastern Cordillera., which, however, is but little known, appears to consist, as in Bolivia, chiefly of Palaeozoic rocks; the western ranges of the Andes are formed of Mesozoic beds, together with recent volcanic lavas and ashes; and the lower hills near the coast are composed of granite, syenite and other crystalline rocks, sometimes accompanied by limestones and sandstones, which are probably of Lower Cretaceous age, and often covered by marine Tertiary deposits.
Farther north, in the department of Ancachs, the Mesozoic belt is composed chiefly of sandstones and shales, and the limestones which form so prominent a feature above Lirna seem to have disappeared.
In the Cordillera Nevada the Mesozoic rocks which form the chain are often covered by masses of modern volcanic rock.
Mesozoic rocks are represented by slates containing Ammoniles and Monotis, evidently of Triassic age, rocks containing Ammonites Bucklandi of Liassic age, a series of beds rich in plants of Jurassic age, and beds of Cretaceous age containing Trigonia and many other fossils.
During the whole of the Mesozoic era Japan appears to have lain on or near the margin of the Asiatic continent, and the marine deposits are confined for the most part to the eastern side of the islands.
In the outer portion of the zone the Permian and Mesozoic beds are crushed and folded against the core of ancient rocks; in the inner portion of the zone they rest upon the old foundation with but little subsequent disturbance.
In the eastern Carpathians also, the Permian and Mesozoic beds are not much folded except near the outer margin of the zone.
In these respects they contrast with the great oceans which owe their origin to the most extensive and the profoundest depressions of the crust, date back at least to Mesozoic times, and have perhaps remained permanently in their present position from still remoter ages.
Mesozoic coals are more abundant in the southern hemisphere, while Tertiary coals seem to be tolerably uniformly distributed irrespective of latitude.
New Zealand includes representatives of all the three Mesozoic systems. The Hokanui group comprises the Triassic Wairoa .and Otapira beds, and the Jurassic Mataura beds.
Along the northern margin lies the intensely folded belt which constitutes the coalfield of Namur, and, beneath the overlying Mesozoic beds, is continued to the Boulonnais, Dover and beyond.
Unlike most Irish counties, Antrim owes its principal features to rocks of Mesozoic and Cainozoic age.
Successive observers in Italy, notably Fracastoro (1483-1553), Fabio Colonna (1567-1640 or 1650) and Nicolaus Steno (1638 - c. 1687), a Danish anatomist, professor in Padua, advanced the still embryonic science and set forth the principle of comparison of fossil with living forms. Near the end of the 17th century Martin Lister (1638-1712), examining the Mesozoic shell types of England, recognized the great similarity as well as the differences between these and modern species, and insisted on the need of close comparison of fossil and living shells, yet he clung to the old view that fossils were sports of nature.
Observing for himself (1794-1800) the stratigraphic value of fossils, he began to distinguish the great Mesozoic formations of England (1801).
Similarly, the Mesozoic reptiles have been traced successively to various parts of the world from France, Germany, England, to North America and South America, to Australia and New Zealand and to northern Russia, from Cretaceous times back into the Permian, and by latest reports into the Carboniferous.
The first exponent of the theory of sudden appearance of new parts and new types, to our knowledge, was Geoffroy St Hilaire, who suggested saltatory evolution through the direct action of the environment on development, as explaining the abrupt transitions in the Mesozoic Crocodilia and the origin of the birds from the reptiles.
It is now applied throughout the Vertebrata of both Mesozoic and Cenozoic times.
Among marine Mesozoic reptiles, each of the groups broadly known as ichthyosaurs, plesiosaurs, mosasaurs and crocodiles were polyphyletic in a marked degree.
The Mesozoic beds are of greater importance.
That these animals were widely distributed in former times is proved by their occurrence at the present day in palaeozoic fossiliferous strata both of the northern hemisphere and of Australia; and despite the fact that their remains have not been found in rocks of the Mesozoic or Kainozoic epochs, it was conceived to be possible that living specimens might be dredged from the sea-floor during the exploration of the ocean depths undertaken by the "Challenger" expedition.
These were followed by a period of minor tilting and faulting in early Mesozoic, by a moderate upwarping in Tertiary, and by a moderate uplift in post-Tertiary time.
The watercourses to-day are, as a rule, longitudinal, following the strike of the weaker strata in paths that they appear to have gained by spontaneous adjustment during the long Mesozoic cycle; but now and again they cross from one longitudinal valley to another by a transverse course, and there they have cut down sharp notches or water-gaps in the hard strata that elsewhere stand up in the long even-crested ridges.
The south-east course of the middle-section rivers is the result of many changes from the initial drainage; the Mesozoic and Tertiary upwarprngs were probably very influential in determining the present general courses.
An important geological characteristic of most of the Cordilferan region is that the Carboniferous strata, which in western Europe and the eastern United States contain many coal seams, are represented in the western United States by a marine limestone; and that the important unconformity which in Europe and the eastern United States separates the Palaeozoic and Mesozoic eras does not occur in the western United States, where the formations over a great area follow in conformable sequence from early Palaeozoic through the Mesozoic.
Farther north in Montana, beyond the gorge of the Missouri river, the structure of the Front Range is altogether different; it is here the carved residual of a great mass of moderately bent Palaeozoic strata, overthrust eastward upon the Mesozoic strata of the plains; instead of exposing the oldest rocks along the axis and the youngest rocks low down on the flanks, the younger rocks of the northern range follow its axis, and the oldest rocks outcrop along its eastern flanks, where they override the much younger strata of the plains; the harder strata, instead of lapping on the mountain flanks in great slab-like masses, as in the Bighorns, form out-facing scarps, which retreat into the mountain interior where they are cut down by outfiowing streams.
The Plateau province, next west of the southern Rocky Mountains, is characterized for the most part by large-textured forms, developed on a great thickness of nearly horizontal Palaeozoic, The Plateau Mesozoic and Tertiary formations, and by a dry climate.
Cretaceous System.This system is much more extensively developed in the United States than any other Mesozoic system.
These great changes in the relation of land and water, and in topography, led to correspondingly great changes in life, and the combination marks the transition from the Mesozoic to the Cainozoic era.
The mountain structures originated in three great orogenic periods, the earliest in the Archean, the second at the end of the Palaeozoic and the third at the end of the Mesozoic. The Archean mountain chains, which enclosed the present region of Hudson Bay, were so ancient that they had already been worn down almost to a plain before the early Palaeozoic sediments were laid down.
The Mesozoic sediments were almost entirely laid down to the west and south-west of the protaxis, upon the fiat-lying Palaeozoic rocks, and in the prairie region they are still almost horizontal; but in the Cordillera they have been thrust up into the series of mountain chains characterizing the Pacific coast region.
This interior plain of the continent represents the area of the ancient sea by which it was occupied in Mesozoic times, with a more ancient margin towards the north-west against the Archean, where undisturbed limestones and other rocks of the Silurian and Devonian rest upon the downward slope of the Laurentian Shield.
In the Mesozoic rocks (Trias and Lias) there have been discovered remains of insects intermediate between those ancient forms and our modern cockroaches, the differentiation between forewings and hindwings having begun.
Outside this arc lies a depression along which the waters of the upper Danube and the lower Rhone find their way towards the sea; and beyond rise the ancient crystalline masses of Bohemia, the Black Forest and the central plateau of France, together with the intervening Mesozoic beds of southern Germany and the Jura.
In the case of the Alps it seems natural enough that the crystalline masses of Bohemia, the Black Forest and the central plateau of France should be firmer than the more modern sedimentary deposits; but it is not so easy to understand why the Mesozoic rocks of southern Germany resisted the folding, while those of the Jura yielded.
The Eastern Alps consist of a central mass of crystalline and schistose rocks flanked on each side by a zone of Mesozoic beds and on the north by an outer band of Tertiary deposits.
On the Italian side there is usually no zone of folded Tertiaries and the Mesozoic band forms the southern border of the chain.
It is intensely folded and is constantly separated from the Mesozoic zone by a fault.
The Mesozoic belt of the Bavarian and Austrian Alps consists mainly of the Trias, Jurassic and Cretaceous beds playing a comparatively subordinate part.
The Mesozoic belt of the southern border of the chain extends from Lago Maggiore eastwards.
The zone of the Molasse is little changed, but the Flysch is partly folded in the Mesozoic belt and no longer forms an absolutely independent band.
Jurassic and Cretaceous beds form the greater part of the Mesozoic band.
On the southern side of the chain the Mesozoic zone disappears entirely a little west of Lago Maggiore and the crystalline rocks rise directly from the plain.
The main chain is formed chiefly of crystalline and schistose rocks, which on the Italian side rise directly from the plain without any intervening zone of Mesozoic beds.
Upon the outer side of the arc the central zone of crystalline rocks is flanked by Mesozoic and Tertiary belts; towards the west, indeed, the individuality of these belts is lost, to a large extent, but the rocks remain.
Upon the inner side the Tertiary band is found only in the eastern part of the chain, while towards the west, first the Tertiary and then the Mesozoic band disappears against the modern deposits of the low land.
The most conspicuous folding, that of the Mesozoic and Tertiary belts, must have occurred in Tertiary times, and it was not completed till the Miocene period.
No Permian beds are known, and for many years Mesozoic deposits were supposed to be entirely absent, but Triassic clays and sandstones with Daonella have been found in the upper part of the basin of the Kwalu (East Sumatra).
Westward the chain lies buried beneath the Mesozoic and Tertiary beds of Belgium and the north of France, but it reappears in the west of England and Ireland.
Geology.Germany consists of a floor of folded Palaeozoic rocks upon which rest unconformably the comparatively little disturbed beds of the Mesozoic system, while in the North German plain a covering of modern deposits conceals the whole of the older strata from view, excepting some scattered and isolated outcrops of Cretaceous and Tertiary beds.
The Monti Peloritani at the north-eastern extremity of the island consists of gneiss and crystalline schists; but with this exception the whole of Sicily is formed of Mesozoic and later deposits, the Tertiary beds covering by far the greater part.
In the southeastern part of the island there are also a few very small outcrops of Mesozoic beds.
The Eocene and Oligocene form a broad belt along the northern coast, very much more continuous than the Mesozoic band, and from this belt a branch extends southwards to Sciacca.
The core is formed by the mountain masses of Rhodope, Belasitza, Perin and Rila; and here Palaeozoic and Mesozoic beds are absent, and the earliest sedimentary deposits belong to the Tertiary period and lie flat upon the crystalline rocks.
The Eastern Cordillera is composed of gneiss, mica and chlorite schist and other crystalline rocks of ancient date; the Western Cordillera, on the other hand, is formed of porphyritic eruptive rocks of Mesozoic age, together with sedimentary deposits containing Cretaceous fossils.
The chief geological formations of Buru are crystalline slate near the north coast, and more to the south Mesozoic sandstone and chalk, deposits of rare occurrence in the archipelago.
Triassic, Jurassic and Cretaceous beds form a band south of the Sea of Marmora, probably the continuation of the Mesozoic band of the Black Sea coast.
Along the coast lies a belt of granite and schist overlaid unconformably by Cretaceous and Tertiary deposits; inland the mountains are formed chiefly of folded Mesozoic beds, together with volcanic rocks of later date.
In the north both the Cretaceous and Tertiary beds of this zone are limited in extent, but towards the south Mesozoic beds, which are at least in part Cretaceous, form a band of considerable width.
The Mesozoic beds are thrown into a series of parallel folds which run in the direction of the chain and which are generally free from any complications such as overthrusting or overfolding.
Through the Mesozoic beds are intruded granitic and other igneous rocks of Tertiary age, and upon the folded Mesozoic foundation rise the volcanic cones of Tertiary and later date.
The Trias is known only at La Ternera near Copiapo, where coal-seams with Rhaetic plants have been found; but the rest of the Mesozoic series, from the Lias to the Upper Cretaceous, appears to be represented without a break .of more than local importance.
The fauna of the Mesozoic beds is very rich, and includes forms which are found in northern Europe, others which occur in central Europe, and others again which are characteristic of the Mediterranean region.
From early Palaeozoic times the peninsula of India has been dry land, a part, indeed, of a great continent which in Mesozoic times extended across the Indian Ocean towards South Africa.
The northern zone is the Tibetan, in which fossiliferous beds of Palaeozoic and Mesozoic age are largely developed - excepting in the north-west no such rocks are known on the southern flanks.
The Mesozoic beds form an irregular triangle extending from Lisbon and Torres Novas on the south to Oporto on the north.
Of the Mesozoic systems the Jurassic is the most widely-spread.
Supposed Triassic beds are found, but they are confined chiefly to the eastern margin of the Mesozoic area north of Lisbon.
The trees are of mesozoic time, though mostly washed down to the foot of the mesas in which they were once embedded, and lying now amid deposits of a later age.
The highlands of New South Wales consist, geographically, of a series of tablelands, now in the condition of dissected peneplains; geologically, they are built of a foundation of Archean and folded Lower Palaeozoic rocks, covered in places by sheets of more horizontal Upper Palaeozoic and Mesozoic rocks; these deposits occur along the edge of the highlands, and are widely distributed on the floor of the coastal districts.
They have been lowered to this level by a monoclinal fold, which has brought down the Mesozoic rocks, so that they extend eastward to the coast, where they dip beneath the sea.
Farther south they disappear beneath the Mesozoic sandstones, from which they again rise along the coast around Lake Illawarra and near the mouth of the Shoalhaven river.
The Mesozoic rocks of New South Wales begin with the Narrabeen Shales; they are covered by the Hawkesbury Sandstones, which are well exposed around Sydney; and they in turn are covered by the Wianamatta Shales.
True Decapods are first met with in Mesozoic rocks, the first to appear being the Penaeidea, a primitive group comprising the Penaeidae and Sergestidae, which occur in the Jurassic and perhaps in the Trias.
It is built up of nearly uniform sheets of Mesozoic rock, the various beds of the Jurassic lying above the New Red Sandstone (Triassic), and dipping south-eastward under the successive beds of the Cretaceous system.
Various lines of reasoning unite in proving that the Mesozoic rocks of the south rest upon a mass of Palaeozoic rocks, which lies at no very great depth beneath the surface of the anticlinal axis running from the Bristol Channel to the Strait of Dover.
Throughout the whole period of its geological history, volcanic activity has found expression with varying degrees of intensity along what is now the western side of the island, with the exception that in the Mesozoic era this activity was in abeyance.
The northern Mesozoic zone is very much broader, and is thrown into simple folds like those of the Jura.
The southern Mesozoic zone is absent, and the Palaeozoic zone sinks abruptly in a series of faulted steps to the plain of the Kura, beneath which no doubt the continuation of the Mesozoic zone is concealed.
Upon the Palaeozoic beds rest a series of Mesozoic deposits, beginning with the Lias and ending with the Upper Cretaceous.
The Mesozoic beds are followed by the Tertiary deposits, which on the Math.
During the Triassic and Jurassic periods the genus Baiera - no doubt a representative of the Ginkgoales--was widely spread throughout Europe and in other regions; Ginkgo itself occurs abundantly in Mesozoic and Tertiary rocks, and was a common plant in the Arctic regions as elsewhere during the Jurassic and Lower Cretaceous periods.
All the Palaeozoic representatives have non-pinnulate arms, while the Mesozoic and later forms have them pinnulate.
Not so, however, when the extinct forms of vertebrate life are taken into consideration, for there is a group of reptiles from the early part of the Secondary, or Mesozoic period, some of whose members must have been so intimately related to mammals that, were the whole group fully known, it would clearly be impossible to draw a distinction between Mammalia on the one hand and Reptilia on the other.
The Harz is a mass of Palaeozoic rock rising through the Mesozoic strata of north Germany, and bounded on all sides by faults.
The Apennines, indeed, consist almost entirely of Mesozoic and Tertiary beds, like the outer zones of the Alps.
On the Italian border of this land there was raised a mountain chain with an inner crystalline zone and an outer zone of Mesozoic and Tertiary beds.
In Calabria the chain consists chiefly of crystalline and schistose rocks; it is the Mesozoic and Tertiary zone which has here been sunk beneath the sea.
Beyond this belt there appear in the north-west Mesozoic limestones, such as occupy so extensive an area in the north-west of the Balkan Peninsula generally, and the valleys opening in that quarter to the Drina have the same desolate aspect as belongs to these rocks in the rest of that region.
The two most important points of contrast between the geology of Ireland and that of England are, firstly, the great exposure of `Carboniferous rocks in Ireland, Mesozoic strata being almost absent; and, secondly, the presence of volcanic rocks in place of the marine Eocene of England.
The volcanic plateaus clearly at one time extended far west and south of their present limits, and the denudation of the lava-flows has allowed a large area of Mesozoic strata also to disappear.
To sum up, then, while the main structural features of Ireland were impressed upon her before the opening of the Mesozoic era, her present outline and superficial contours date from an epoch of climatic and geographical change which falls within the human period.
On the flanks of the primitive western axis certain ancient sedimentary strata are thrown into folds which were completed before the commencement of the mesozoic period.
In the south, the later palaeozoic rocks are also thrown into acute folds by a movement acting from the south, and which ceased towards the close of the mesozoic period.
None of these earth movements affected the interior, for here the continental mesozoic deposits rest, undisturbed by folding, on the primary sedimentary and crystalline rocks.
The formations older than the mesozoic are remarkably unfossiliferous, so that the determination of their age is frequently a matter of speculation, and in the following table the European equivalents of the pre-Karroo formations in many regions must be regarded as subject to considerable revision.
The Crystal Mountains of Angola may represent its western boundary; while the absence of mesozoic strata beneath the Cretaceous rocks of the mid-Sahara indicates that the system of Karroo lakeland had here reached its most northerly extension.
The faunal aspect of the Tertiary periods differs strikingly from that of preceding Secondary or Mesozoic; in place of the great saurian reptiles we find the rapid development and finally the maximum expansion of mammals.
Geology.Geologically the Spanish Peninsula consists of a great massif of ancient rock, bordered upon the north, east and south by zones of folding in which the Mesozoic and early Tertiary beds arc involved.
Settlement of population has taken place principally among the plains and lower levels of the north-western, midland and south-eastern parts of the island, following in the main the rocks of Tertiary and Mesozoic age.
The most conspicuous member of the Mesozoic group is the sheet of diabase and dolerite, made up of laccolites and sills, which covers most of the central plateau of Tasmania.
West of the great valley the range is composed of Mesozoic beds, together with Tertiary volcanic rocks.
Sometimes they rise from the Mesozoic zone of the western Cordillera, sometimes from the ancient rocks of the eastern zone.
At a more recent horizon, the silicified specimens of the Mesozoic Gymnosperms from Great Britain, France, and especially North America, are no less important.
The Glossopteris flora of India and the southern hemisphere, the age of which has been disputed, but is now regarded as for the most part Permo-Carboniferous, is, however, dealt with in the succeeding section, in connexion with the Mesozoic floras.
There is no evidence that the Angiospermous flowering plants, now the dominant class, existed during the Palaeozoic period; they do not appear till far on in the Mesozoic epoch, and their earlier history is as yet entirely unknown.
There is, however, some evidence that Isoetes, which in several respects agrees more nearly with the Lepidodendreae, may actually represent their last degenerate survivors (see Pleuromeia, in § II., MEsozoic).
The curious male sporophylls may perhaps be remotely comparable to those recently discovered in Mesozoic Cycadophyta, of the group Bennettiteae.
Mesozoic The period dealt with in this section does not strictly correspond with that which it is customary to include within the limits of the Mesozoic system.
The Mesozoic era, as defined in geological textbooks, includes the Triassic, Jurassic and Cretaceous epochs; but from the point of view of the evolution of plants and the succession of floras, this division is not the most natural or most convenient.
Our aim is not simply to give a summary of the most striking botanical features of the several floras that have left traces in the sedimentary rocks, but rather to attempt to follow the different phases in the development of the vegetation of the world, as expressed in the contrasts exhibited by a comparison of the vegetation of the Coal period forests with that of the succeeding Mesozoic era up to the close of the Wealden period.
We must begin by briefly considering this southern Palaeozoic province if we would trace the Mesozoic floras to their origin, and obtain a connected view of the vegetation of the globe as it existed in late Palaeozoic times and at the beginning of the succeeding era.
From strata in New South Wales overlying Devonian and Lower Carboniferous rocks certain plants were discovered in the early part of the 19th century which were compared with European Jurassic genera, and for several years it was believed that these plant-beds belonged to the Mesozoic period.
These supposed Mesozoic plants include certain genera which are of special interest.
This continental area has been described as " Gondwana Land," a tract of enormous extent occupying an area, part of which has since given place to a southern ocean, while detached masses persist as portions of more modern continents, which have enabled us to read in their fossil plants and ice-scratched boulders the records of a lost continent in which the Mesozoic vegetation of the northern hemisphere had its birth.
Having seen how the Glossopteris flora of the south gradually spread to the north in the Permian period, we may now take a brief survey of the succession of floras in the northern hemisphere, which have left traces in Mesozoic rocks of North America, Europe and Asia.
It is probable that the Jurassic Goniolina, described from French localities, and other genera which need not be mentioned, may also be reckoned among the Mesozoic Siphoneae.
It is hardly too much to say that no absolutely trustworthy examples of Mosses have so far been found in Mesozoic strata.
This genus, like the allied Calamites, appears to have possessed cones of more than one type; but we know little of the structure of these Mesozoic Equisetaceous genera as compared with our much more complete knowledge of Calamites and Archaeocalamites.
Among the large number of Mesozoic Ferns there are several species founded on sterile fronds which possess but little interest Filicales, from a botanical standpoint.
It is of interest to note that some leaf-fragments recently found in Permian rocks of Kansas, and placed in a new genus Glenopteris, are hardly distinguishable from specimens of Jurassic and Rhaetic age referred to Thinnfeldia and other Mesozoic genera.
The scaly ramenta which occur in abundance on the leaf-stalk bases of fossil Cycads constitute another fern-character surviving in Mesozoic Cycadales.
Without a fuller knowledge of internal structure and of the reproductive organs, we are compelled to speak of some of the Mesozoic plants as possibly Ferns or possibly Cycads, and not referable with certainty to one or other class.
The abundance of Palaeozoic plants with sporangia and sori of the Marattiaceous type is in striking contrast to the scarcity of Mesozoic ferns which can be reasonably included in the Marattiaceae.
The Osmundaceae, represented by a few forms of Palaeozoic age, played a more prominent part in the Mesozoic floras.
The recent genus, Dipteris, with its four existing species, occurring .chiefly in the Indo-Malayan region (Map B, Dipteris), is also a modern survival of several Mesozoic types represented.
The Dip teridinae are represented also by species from Mesozoic rocks of Persia (Map B, D 2), Greenland (Map B, D 3), North America (D 4), South America (D 5) and China (D6).
The Cyatheaceae constitute another family of leptosporangiate Ferns which had several representatives in Mesozoic floras.
On the other hand, there are several fossil Ferns of Jurassic age possessing cup-like sori like those of Thyrsopteris and other Cyatheaceous Ferns, which indicate a wide Mesozoic distribution for this family.
It is a striking fact that among the numerous Mesozoic Ferns there are comparatively few that can with good reason be referred to the Polypodiaceae, a family which plays so dominant a role at the present day.
The majority of the specimens included in the genus Cladophlebis, the Mesozoic representative of the Palaeozoic Pecopteris type of frond, are known only in a sterile condition, and cannot be assigned to their family position.
The abundance of Cycadean plants is one of the most striking features of Mesozoic floras.
With regard to the distinguishing features and the distribution of the numerous Cycadean leaves of Mesozoic age, the most striking fact is the abundance of as well in North America, throughout Europe.
The majority of Mesozoic stems agree in external appearance with those of recent species of Encephalartos, Macrozamia, and some other genera; the trunk is encased in a mass of persistent petiole-bases separated from one another by a dense felt or packing of scaly ramenta.
The best preserved specimens of the true Bennettites type so far described are from the Lower Greensand and Wealden of England, and from Upper Mesozoic strata in North America, Italy and France.
This form of stem, of a habit entirely different from that of recent Cycads and extinct Bennettites, points to the existence in the Mesozoic era of another type of Gymnosperm allied to the Bennettitales of the Jurassic and Cretaceous periods by its flowers, but possessing a distinctive character in its vegetative organs.
There is no doubt that the Cycadophyta, using the term suggested by Nathorst in 1902, was represented in the Mesozoic period by several distinct families or classes which played a dominant part in the floras of the world before the advent of the Angiosperms. In addition to the bisporangiate reproductive shoots of Bennettites, distinguished by many important features from the flowers of recent Cycads, a few specimens of flowers have been discovered exhibiting a much closer resemblance to those of existing Cycads, e.g.
Both Tertiary and Mesozoic localities are indicated in the map.
An adequate account of fossil Mesozoic Conifers is impossible within the limits of this article.
Coniferous twigs are very common in Mesozoic strata, but in most cases we are compelled to refer them to provisional genera, as the evidence of vegetative shoots alone is not sufficient to enable us to determine their position within the Coniferae.
Fossil wood, described under the name Cupressinoxylon, has been recorded from several Mesozoic horizons in Europe and elsewhere, but this term has been employed in a wide sense as a designation for a type of structure met with not only in the Cupressineae, but in members of other families of Coniferae.
The two surviving species of Sequoia afford an illustration of the persistence of an old type, but unfortunately most of the Mesozoic species referred to this genus do not possess sufficiently perfect cones to confirm their identification as examples of Sequoia.
There are a few points suggested by a general survey of the Mesozoic floras, which may be briefly touched on in conclusion.
It is in rocks of Upper Triassic and Rhaetic age that abundant remains of rich floras are met with, and an examination of the general features of the vegetation reveals a striking contrast between the Lower Mesozoic plants and those of the Palaeozoic period.
The change to this newer type of vegetation was no doubt less sudden than it appears as read from palaeobotanical records, but the transition period between the Palaeozoic type of vegetation and that which flourished in the Lower Mesozoic era, and continued to the close of the Wealden age, was probably characterized by rapid or almost sudden changes.
In the southern hemisphere the Glossopteris flora succeeded a Lower Carboniferous vegetation with a rapidity similar to that which marked the passage in the north from Palaeozoic to Mesozoic floras.
The difference between the Glossopteris flora and those which have left traces in the Upper Gondwana rocks of India, in the Wianamatta and Hawkesbury beds of Australia, and in the Stormberg series of South Africa is much less marked than that between the PermoCarboniferous flora of the northern hemisphere and the succeeding Mesozoic vegetation.
At a later stage - in postWealden days - it was the appearance of Angiosperms, probably in northern latitudes, that formed the chief motive power in accelerating the transition in the fades of plant-life from that which marked what we have called the Mesozoic floras, to the vegetation of the Upper Cretaceous and Tertiary periods.
Among modern floras we find here and there isolated types, such as Ginkgo, Sequoia, Matonia, Dipteris and the Cycads, persisting as more successful survivals which have held their own through the course of ages; these plants remain as vestiges from a remote past, and as links connecting the vegetation of to-day with that of the Mesozoic era.
References to important papers on Mesozoic botany will be found in the bibliographies mentioned in the above list.
Recession of the plateaux margins has exposed underlying Mesozoic strata and, in some areas, the Paleozoic basement.
The MT survey confirmed the existence of a Mesozoic sedimentary basin between lava flows and the Precambrian basement.
In general, Cretaceous greensands and limestones or Tertiary basalts rest unconformably on a range of older Mesozoic rock units.
Dinosaurs were one of several groups of prehistoric reptiles that lived during the Mesozoic Era, the " Age of Reptiles.
During the Mesozoic, most of central and western Thailand was affected by large, left lateral wrench faults and compressional tectonics.
Important material of early Mesozoic tetrapods was deposited in the collections by N.C. Fraser, who worked in the Museum in the 1980's.
In the eastern region the Trias is entirely absent and the Mesozoic series begins with the Upper Jurassic.
Some of the most profound changes that have taken place on this globe occurred in Mesozoic times, and a great portion of Australia was already dry land when vast tracts of Europe and Asia were submerged; in this sense, therefore, Australia has been rightly referred to as one of the oldest existing land surfaces.
They are best developed in the Macdonnell chain in Palaeozoic U Mesozoic Dolerite '&c. ' ® central Australia and in Victoria, where the fullest sequence is known; while they also extended north-eastward from Victoria into New South Wales, where, as yet, no Cambrian rocks have been found.
The Upper Carboniferous period was in the main terrestrial, and during it were laid down the coal-seams of New South Wales; they are best developed in the basin of the Hunter river, and they extend southward, covered by Mesozoic deposits, beyond Sydney.
Freshwater and terrestrial deposits of Mesozoic age occur in many places, and the conclusion is irresistible that the greater part of this area has been land since the close of the Palaeozoic era.
The more resistant rocks, even though dissected by Tertiary erosion, retain in their summit tiplands an indication of the widespread peneplain of Cretaceous tinie, now standing at the altitude given to it by the Tertiary upwarping and post-Tertiary uplift; and the most resistant rocks surmount the Cretaceous peneplain as unconsumed monadnocks of the Mesozoic cycle.
To the west and south-west the general character of the land changes; the ends of the Tertiary beds are raised in small hills and Mesozoic rocks appear, forming broken ridges of the Pre-Cordillera, a name given on the continent to the ridges which precede, to the east, the Andes.
The history of the Ginkgoales will be found in the Mesozoic section of this article (see also Gymnosperms); their nearest Palaeozoic representatives " were probably members of the Cordaitales, an extinct stock with which the Ginkgoaceae are closely connected " (Seward).
Dinosaurs were one of several groups of prehistoric reptiles that lived during the Mesozoic Era, the Age of Reptiles.
In the eastern region this was the last folding which has affected the country, and the Mesozoic and Tertiary beds are almost undisturbed.
In the western region, on the other hand, all the Mesozoic beds are involved in a later system of folds; but here also the Tertiary beds lie nearly horizontal.
There were, therefore, two principal epochs of folding in the island, one at the close of the Palaeozoic era which affected the whole of the island, and one at the close of the Mesozoic which was felt only in the western region.
It confirms the general belief on geological grounds that this was the seat of their development at the close of the Mesozoic era.
Between India and China there is a broad belt in which marine deposits of Mesozoic and Tertiary age are well developed.
On the other hand, limestone and sandstone, especially of the Mesozoic strata, are strikingly deficient.
South and west of the Fossa Magna the beds are thrown into folds which run approximately parallel to the general direction of the coast, and two zones may be recognizedan outer, consisting of Palaeozoic and Mesozoic beds, and an inner, consisting of Archaean and Palaeozoic rocks, with granitic intrusions.
His contributions on the Mesozoic reptiles of Great Britain culminated in his complete rearrangement and classification of this group, one of his greatest services to palaeontology.