The principal rocks are andesites, but trachytes and basalts are also common.
The rocks are mainly basalts and andesites, together with trachytes and phonolites, and some of the basaltic flows are of enormous extent.
Trachytes, rhyolites, andesites and basalts occur, and a definite order of succession has been made out in several areas; but this order is not the same throughout the chain.
The building up of these domes of lavas of intermediate chemical type was followed by the eruption of sheets of andesites and rhyolites in the Thames English Miles so Ioo 200 Cretaceous 'a '
Among the Tertiary volcanic rocks those of acid types (granites, granulites) were the first to appear and are developed latitudinally; rocks of intermediate type (dacites, andesites) characterize the Miocene and early Pliocene periods; while the basic rocks (ophites, elaeolite syenites and basalts) attained their maximum in later Pliocene and Quaternary times.
In the Miocene period andesites of various kinds were erupted, while at the close of the Pliocene began the great eruptions of basalt which reached their maximum in Quaternary times and continue to the present day.'
Basic lavas, with andesites, trachytes, tuffs and agglomerates are the most common Scottish rocks of this period.
Both Great and Little Ararat consist entirely of volcanic rocks, chiefly andesites and pyroxene andesites, with some obsidian.
The whole of this consists of tuffs and lavas, andesites prevailing in the west and rhyolites and dacites in the east.
We may note the pre-Cambrian lavas and tuffs of the Wrekin district in Shropshire and the somewhat later volcanic rocks of Charnwood; the porphyrites, andesites, tuffs and rhyolites of the Borrowdale volcanic centre, erupted in the Ordovician period, and the Silurian granites of the same region.
The cones themselves are composed largely of acid andesites, but many of the lavas are augite andesites and basalts.
Cretaceous Jurassic N k Bodorno :s: Vladikaukaz Lars `n - - - n ° Tiflis a =Plain of Vladikaukaz; b= Upper Jurassic; Moraine terrace; d= Folded lias shales; e = Upper Jurassic; = Paleozoic schists; Creenstone dykes; h= Granite; g°= Gneiss; i = Andesites; k = Jurassic?; I = Pliocene fNagelfluh); m = Miocene; 11 = Oligocene; r = Nullipore limesto n e & conglomerate.
While upheavals having a north-eastern strike continued to take place after the Carboniferous epoch,' another series of upheavals, having a north-western strike, and occasioned by the expansion of diabases, dolerites, melaphyres and andesites, occurred later, subsequently at least to the close of the Tertiary period, if not also before it, dislocating former chains and raising rocks to the highest levels by the addition of new upheavals to the older ones.
A large exposure of this Old Red Sandstone stretches from Enniskillen to the Silurian beds at Pomeroy, and some contemporaneous andesites are included, reminding us of the volcanic activity at the same epoch in Scotland.