Ten shafts lined with slabs of tufa which were there found may have been the approaches to tombs or may have served as wells.
Calcareous tufa or travertine occurs in the valley of Matlock and elsewhere, the southern part of the county, from Matlock southward by Heage, Belper and Duffield to Derby.
Calcareous tufa or travertine occurs in the valley of Matlock and elsewhere, and in some places is still being deposited by springs.
By abrupt tufa cliffs; but a massive wall found by excavation on the S.W.
64) was the first to fix the site upon the low hill, surrounded by tufa cliffs, on which were still scanty remains of walling in rectangular blocks of the same material, which is now occupied by the farm-house of Conca.
Catacomb of benches cut out of the tufa rock.
The igneous formation of which the greater part of the Roman Campagna is, in its superior portion, composed, contains three strata known under the common name of tufa, - the " stony," " granular," and " sandy " tufa, - the last being commonly known as pozzolana.
The stony tufa (tufa litoide) is quarried as building-stone.
The granular tufa is useless for either purpose, containing too much earth to be employed in making mortar, and being far too soft to be used as stone for building.
16) from Marchi's work, when compared with that of the catacomb of Sant' Agnese already given, presents 1 In Rome the three strata are known to geologists as tufa litoide, tufa granolare and pozzolana.
To adapt the ground for its purpose as a cemetery, a gallery was run all round the area in the tufa rock at a convenient depth below the surface, reached by staircases at the corners.
The site, surrounded by ravines and accessible only on the W., is naturally strong and characteristic of an Etruscan town; on this side there is a considerable fragment of the ancient Etruscan wall, built of rectangular blocks of tufa (whether the rest of the site was protected by walls is uncertain), and a ruined castle, erected by Antonio da Sangallo the elder in 1499, for Pope Alexander VI., and restored by Pope .Paul III.
The Mithraeum hewn in the tufa quarries of the Capitoline Hill at Rome, still in existence during the Renaissance, is an example.
In 1846 he began experiments on the temperature of the earth at different depths and in different soils near Edinburgh, which yielded determinations of the thermal conductivity of trap-tufa, sandstone and pure loose sand.
There are some remains of the ancient city walls of rectangular blocks of tufa on the southern side of the town, and some rock-cut sewers in the cliffs below them.
On the former there are now no traces of antiquity, but on the latter are scanty remains of the city walls, in small blocks of the grey-green tufa (cappellaccio) which is used in the earliest buildings of Rome, and traces of the streets.
Cinder cones and tufa cones abound, but one of the most distinguishing features of the Hawaiian volcanoes is the great number of craters of the engulfment type, i.e.
It was defended by a deep ditch, which can still be traced, and by walls, a portion of which, on the eastern side, constructed of rectangular blocks of tufa, was brought to light in 1897.
In the second period volcanic activity occurred at the bottom of the Pliocene sea, and the tufa, which extends over the whole Campagna to a thickness of 300 ft.
The tufa, sperone and peperino were easy to quarry, and could be employed by those who possessed comparatively elementary tools, while travertine, which came into use later, was an excellent building stone, and the lava (selce) served for paving stones and as material for concrete.
The subsoil too is differently formed: the surface consists of very absorbent materials, then comes a stratum of less permeable tufa or peperino (sometimes clay is present), and below that again more permeable materials.
Wide, which ran, not at the bottom of the valleys, where there were sometimes streams already, and where, in any case, erosion would have broken through their roofs, but along their slopes, through the less permeable tufa, their object being to drain the hills on each side of the valleys.
As the drainage by cuniculi removed the moisture in the subsoil, so the drainage of the lakes by emissaria, outlet channels at a low level, prevented the permeable strata below the tufa from becoming impregnated with moisture which they would otherwise have derived from the lakes of the Alban Hills.
It appears, however, from a careful examination of the remains that their work was only a reconstruction of a more ancient edifice, the date of the original form of which cannot be fixed; while its first alteration belongs to the "tufa" period, and three other periods in its history can be traced.
No good building stone was at hand; and the public as well as private edifices were constructed either of volcanic tufa, or lava, or Sarno limestone, or brick (the latter only used for the corners of walls).
In a few instances only do we find them making use of a whitish limestone wrongly called travertine, which, though inferior to the similar material so largely employed at Rome, was better adapted than the ordinary tufa for purposes where great solidity was required.
Grey tufa period; ashlar masonry of tufa, coated with fine white stucco; rubble work of lava.
No homogeneous series of buildings - we find various styles of construction (quasi-reticulate, opus reticulatum of tufa with stone quoins, of the time of Augustus, opus reticulatum with brick quoins or with mingled stone and brick quoins, a little later); and three styles of wall decoration fall within its limits.
They are mostly of volcanic origin, and include pumice, tufa, santorin earth, trass and pozzuolana itself.
Generally speaking, they are only of local importance, their cheapness depending largely on the nearness and abundance of some suitable volcanic deposit of the trass or tufa class.
In section the isle is seen to possess a threefold character: there is first a basement of tufa, from which rise, secondly, colonnades of basalt in pillars forming the faces and walls of the principal caves, and these in turn are overlaid, thirdly, by a mass of amorphous basalt.
But its most notable article of commerce is that of mill-stones, made of lava and tufa-stone, a product much used by the Dutch in the construction of their dykes.
In the part of Herculaneum already excavated the corridors in the upper portions of the theatre are compactly filled, up to the head of the arches, with pozzolana and pumice transformed into tufa (which proves that the formation of this stone may take place in a comparatively short time).
Tufa is also found in the lowest part of the city towards the sea in front of the few houses that have been discovered; and in the very high banks that surround them, as also in the lowest part of the theatre, there are plainly to be seen earth, sand, ashes, fragments 3 C.I.L.
Of country (in the beginning very steep, and at intervals almost level), where certainly it would have been arrested and all accumulated in a mound; but it must have been borne along by a great quantity of water, the effects of which may be distinctly recognized, not only in the filling and choking up even of the most narrow, intricate and remote parts of the buildings, but also in the formation of the tufa, in which water has so great a share; for it cannot be supposed that enough of it has filtered through so great a depth of earth.
The site of the primitive city, which later became the citadel, is occupied by the modern town; it is situated at the end of a long plateau between two valleys, and protected by perpendicular tufa cliffs some 60 ft.
Here it is defended by a fine wall of opus quadratum of tufa, in alternate courses of headers and stretchers.
It took the place of an earlier one, of similar proportions but built of tufa or "poros" stone.
They are well constructed of regular parallelograms of a sandy tufa, laid in headers and stretchers.
The main part of the town and the bazaars are crowded alongside the stream, while suburbs with scattered houses among orchards and gardens extend up two tributary streams. The houses are massive and well built of a soft volcanic tufa, and with their courtyards and gardens climbing up the hillsides afford a striking picture.
Remains of the city walls, built of blocks of tufa 2 ft.
The town lay on a hill of tufa, running from N.E.
The line of the city walls, of rectangular blocks of tufa, can be traced, and there seem to have been eight gates in the circuit, which was about 4 m.
On the right bank they are of pliocene gravel, on the left of tufa; and on the latter, on a cliff above the river (the ancient Puilia saxa) stood Ficana (marked by the farmhouse of Dragoncello), which is said to have owed its origin to Ancus Martius.
Outflows of lava and tufa cover the mountain sides and fill up the valleys.
East of Paris, an isolated deposit of calcareous tufa full of leaves, which gives a curious insight into the vegetation which flourished in Paleocene times around a waterfall.