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We may hence conclude that when a sandy soil is stripped of wood, the local temperature will be raised. After the sands follow successively argillaceous, arable, and garden ground, then humus, which occupies the lowest rank. "The retentive power of humus is but half as great as that of calcareous sand. We will add that the power or retaining heat is proportional to the density.
Limestones are rare in this series, but one band of 300 feet in thickness has been traced for considerable distances to the north of Lake Huron. Beds of greenstone are intercalated conformably with the quartzose and argillaceous members of this series. No organic remains have yet been found in any of the beds, which are about 18,000 feet thick, and rest unconformably on the Laurentian rocks.
As there is, in this country of Scotland, two different species of mountains or hills, one composed both in matter and manner exactly similar to the Alps of Switzerland, the other of whin-stone, basaltic rock, or subterraneous lava; and as the fossil coal, argillaceous and sand-stone strata, are found variously connected with those hills, nothing can tend more to give a proper understanding, with regard to the construction of the land in general, of the globe than a view of those different bodies, which are here found much mixed together in a little space of country, thus exhibiting, as it were in miniature, what may be found in other parts of the world, upon a larger scale, but not upon any other principle.
Among the lowest species of this combustible schistus are those argillaceous strata in Yorkshire from whence they procure alum in burning great heaps of this stone, which also contains sulphur, to impregnate the aluminous earth with its acid.
A well-known substance, called bog-iron ore, often met with in peat-mosses, has often been shown by Ehrenberg to consist of innumerable articulated threads, of a yellow ochre colour, composed of silica, argillaceous matter, and peroxide of iron. Layers of this iron ore occurring in Scotch peat bogs are often called "the pan," and are sometimes of economical value.
The argillaceous dust accumulated on the Kasveen plain by the weathering of the surrounding uplands resembles in appearance the “yellow earth” of the Hoang Ho district in China, but remains sterile for the lack of water.
These rocks consisted of quartzose and schistose beds, the first of which supplied white sand and the other argillaceous mud to a river which entered the sea at this point, carrying down in its turbid waters much drift-wood and the leaves of plants.
It has evidently been formed of such argillaceous and siliceous materials, not only indurated, so as to lose its character, as an argillaceous stone, but to have been brought into that degree of fusion which produces perfect solidity. Of the same kind are those hornstein rocks of the nature of flint, sometimes tending to the nature of a fine sandstone.
At eighty miles from the coast, in a cliff thus composed, there were a few layers of ferruginous sandstone, and of an argillaceous sandstone with concretions of marl like those in the Pampas. The strata generally dipped at an angle of 45 degrees towards the cliff from which they had slided. I have observed in slips, both on a small and large scale, that this inward dip is very general.
The uppermost part, judging from the rocks near the famous silver mine of Huantajaya, consists of laminated, impure, argillaceous, purplish-grey limestone, associated, I believe, with some purple sandstone.
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