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Above these porphyries comes a coarse, arenaceous conglomerate, the lower half white and the upper half of a pink colour, composed chiefly of pebbles of various porphyries, but with some of red sandstone and jaspery rocks. In some of the more arenaceous parts of the conglomerate, there was an oblique or current lamination; a circumstance which I did not elsewhere observe.
The sole, a broad expanse of loose red arenaceous matter, the washings of the plateau, is fearfully burrowed and honeycombed; it is also subject, like its sister the Sadr, to the frequent assault of "devils," or sand-pillars. That it is plentifully supplied with water, we learn from the presence of birds.
In the eastern half, near Maldonado, this deposit is more arenaceous than in the Pampas, it contains many though small concretions of marl or tosca-rock, and others of highly ferruginous sandstone; in one section, only a few yards in depth, it rested on stratified sand.
Here again we meet with that precipitous, inaccessible kind of country which distinguishes the sandstone formation, so extensive in Australia. This arenaceous deposit, for a long time, confined the colonists within the line of the Hawkesbury, and until the want of fresh pastures during dry seasons compelled them to explore these rocky regions.
Similar elongated processes have been also observed to extend from the shells of some Belemnites discovered by Dr. The arenaceous limestone which passes under this name is generally grouped as a member of the Oxford clay, in which it forms, in the south-west of England, lenticular masses, 8 or 10 feet thick, containing at Kelloway, in Wiltshire, numerous casts of ammonites and other shells.
The phenomenon that had broken over the arenaceous couch, upon which slept the four castaways, was neither more nor less than a "sandstorm"; or, to give it its Arab title, a simoom.
The arenaceous laminae are much hardened at the point of contact, and the clays are converted into siliceous schist. In this island the altered rocks assume a honey-comb structure on their weathered surface, singularly contrasted with the smooth and even outline which the same beds present in their usual soft and yielding state.
The presence of cyanite, rutile-titanite, and garnets, and the absence of Lydian stone, and all fragmentary or arenaceous rocks, seem to characterise the formation we describe as primitive. It is asserted that even in Europe ampelite and green stone are found, though rarely, in slates anterior to transition-slate.
Laramie Plains present a broad bottom on both sides of the river, comprising about twelve hundred square miles, bounded on the north and east by the Black Hills, on the south by a "divide" of arenaceous rock, embedded in marl and white clay, almost barren of verdure, while on the west are the beautiful Medicine Bow Mountains.
Calcareous sand is then formed from comminuted shell and coral, or, in some cases, arenaceous matter replaces the clay; because it commonly happens that the finer sediment, being first drifted farthest from coasts, is subsequently overspread by coarse sand, after the sea has grown shallower, or when the land, increasing in extent, whether by upheaval or by sediment filling up parts of the sea, has approached nearer to the spots first occupied by fine mud.
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