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This earthy mass is of a pale reddish colour, like the less pure varieties of Pampean mud in Banda Oriental; it includes small calcareous concretions, like those of tosca- rock but more arenaceous, and other concretions of a greenish, indurated argillaceous substance: a few pebbles, also, from the underlying gravel-bed are also included in it, and these being occasionally arranged in horizontal lines, show that the mass is of sub-aqueous origin.
Where the pebbles off the shore are plenty, a rocky beach may be produced by this process of importation through the agency of seaweeds without any supply being brought by the waves along the coast line. Returning to sand beaches, we enter the most interesting field of contact between seas and lands. Probably nine tenths of all the coast lines of the open ocean are formed of arenaceous material.
It was not quite an hour, however, since the commencement of the sandstorm; and yet, in this short time, the arenaceous dust had accumulated to the thickness of several inches upon their bodies; and a person passing the spot, or even stepping right over them, could not have told that four human beings were buried beneath; that is, upon the supposition that they would have lain still, and not got startled from their slumbers by the foot thus treading upon them.
Great as is the diversity in the horizontal extent of individual coal-seams, they all present one characteristic feature, in having, each of them, what is called its UNDERCLAY. These underclays, co-extensive with every layer of coal, consist of arenaceous shale, sometimes called fire-stone, because it can be made into bricks which stand the fire of a furnace.
The upper half of the cliff, to a thickness of about thirty feet, consists of Pampean mud, of which the lower part is pale-coloured, and the upper part of a brighter red, with some irregular layers of an arenaceous variety of tosca, and a few small concretions of the ordinary kind.
Parts pass into a very pale green, semi- porcellanic stone. Ninthly: red or brown coarse conglomerate, three or four hundred feet thick, formed chiefly of pebbles of porphyries, with volcanic particles, in an arenaceous, non-calcareous, fusible basis: the upper two feet are arenaceous without any pebbles.
Yet there is a great change in the materials of the rocks of the two formations, shewing that while the bottoms of the seas of the one period had been chiefly arenaceous, those of the other were chiefly clayey and limy. And there is an equal difference between the two periods in respect of both botany and zoology.
The boulders of Erreré are entirely distinct from the rock of the Serra, and consist of masses of compact hornblende. It would seem that these two ranges skirting a part of the northern and southern banks of the Lower Amazons are not the only remnants of this arenaceous formation in its primitive altitude.
On an arenaceous strip projecting from the western edge the women were washing and panning where the bottom of the digging was below that of the river. This is an everyday sight on the Ancobra, and it shows what scientific 'hydraulicking' will do.
The loftiest of the Cyclopean islets, or rather rocks, is about 200 feet in height, the summit being formed of a mass of stratified clay, the laminae of which are occasionally subdivided by thin arenaceous layers. Newer Pliocene strata invaded by lava. Lava. b. Laminated clay and sand. c.
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