The rocks on the verge of the Kisumu province of East Africa are mainly volcanic (basalt, tuff, lava, kenyte).
Like the rest of the cluster, the island is of volcanic origin, with tuff, trachyte and obsidian among its ordinary rocks.
In the Rudolf province there and are the basalt, lava, tuff and kenyte of the volcanic mineralogy.
Tuff and travertine are calcareous deposits found in volcanic districts.
The top of the heads of the images is cut flat to receive round crowns made of a reddish vesicular tuff found at a crater about 8 m.
Occasional beds of tuff are intercalated among these lavas, and likewise seams of fine clay or shale which have preserved the remains of numerous land-plants.
Flowing in a deep bed cut in the tuff strata, the river is not navigable.
(6) South Sumatra, so far as known, presents everywhere in its valleys the same character as that of the Batang Toru, Batang Gadis, Sumpur, &c. They also are closed in on the north and south by volcanoes "which have here produced similar masses of tuff, with lakes and rivers of the same formation as in the north.
Varieties of basaltic lava and tuff containing little or no olivine - the rock type known as labradorite.
The remarkable stability of the mountain appears to be due to the innumerable dikes which penetrate the lava flows and tuff beds in all directions and thus bind the whole mass together.
Where lava has been piled up in successive nearly horizontal sheets, with occasional layers of tuff or other softer rock between them, it offers conditions peculiarly favourable for the formation of escarpments, as in the wide basalt plateaus of the Inner Hebrides.
The lavas are usually porphyrites, which occur in sheets, with intercalated bands of volcanic tuff that are sometimes strongly felsitic. One of the vents by which such materials were ejected occurs in the Braid Hills on the south side of Edinburgh.
At the base there is frequently a conglomerate or tuff of porphyritic rocks.
In the middle of Iceland, where the geological foundation is tuff and breccias, large areas are buried under ancient outflows of lava, which bear evidences of glacial scratching.
Basalt and tuff, probably of Tertiary age, form the great mass of the Cameroon mountain, also the island of Fernando Po.
The latter are represented by large contemporaneous deposits of tuff and felsitic lava which in the Snowdon District are several thousand feet thick.
In the vicinity of the Ullughmuz-tagh there exist numerous indications of former volcanic activity, the eminences and summits frequently being capped with tuff, and smaller fragments of tuff are scattered over other parts of the Arka-tagh ranges.
They consist, in most parts of the country, of unconsolidated sediments, consisting of gravel, sand, clay, &c., together with large quantities of tuff, volcanic agglomerate, &c. Some of the sedimentary formations are of marine, some of brackish water, and some of terrestrial origin.
Large areas are overlain with trachyte, basalt, obsidian, tuff and pumice.
Granby tuff 580,,
Two systems. At the close of the Cretaceous period great eruptions of basalt and basaltic tuff took place, especially in the Lisbon area.