Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/522

 terrestrial remains of easy explanation, without accepting the theory of subaerial formation : a shell or other animal relic has only to drop into a fissure or be carried down by a stream of water during a flood ; the soil around readily adapts itself to its shape, fills its interstices, and, in fact, in a short time loses so completely all trace of having been disturbed, that the shell or other substance becomes a pseudo-fossil. On the other hand, if the foreign substances were really contemporaneous with the mass, they would most probably be found constituting the centre of aggregation in the calcareous nodules spoken of. I have broken open probably some hundreds of these, and never found a trace of fossils. The Loess, as I have suggested above, bears, in some respects, a mechanical resemblance to chalk. These are the extreme fineness of the particles of which it is composed, the presence of vertical tubes leading downwards from the surface, and the occurrence of nodules like the "potstones " in the chalk, with their major axes vertical. The large amount of carbonate of lime in its composition is also worthy of note in the comparison. All these reasons seem to suggest a similar origin for the two formations — namely, on the bed of a tranquil sea.

Baron von Richthofen (I believe rightly) rejects the theory of the Loess being of freshwater origin, as requiring a freshwater lake of such enormous proportions that we cannot believe in its existence at any period. The shape of the older mountain-chains, and their peculiar weathering, he argues, forbid the supposition of glacial action. (See my former paper, Quart. Journ. Geol. Soc. vol. xxv. p. 137.)

Materials of the Loess. — In stating some of my grounds for coming to the conclusion that the Loess is a true marine formation, I have incidentally mentioned many objections to its subaerial origin as suggested by Baron von Richthofen. There are, however, others of even stronger nature. Its chemical composition, consisting, as it does, mainly of silicates of alumina and of free silica in the condition of impalpable sand, does not correspond with that of the inorganic elements of plants growing on its surface. Granting, however, that the earthy carbonates and a portion of the silica could be derived from such a source, whence could the plants themselves derive these elements, but in turn from the soil on which they grew ? Lime, potassa, magnesia, iron, and silica might, then, so long as the plant had access to subjacent formations, or was supplied by springs from below, have been deposited in a superficial layer ; silica might even, as suggested, have been conveyed by the medium of duststorms ; but whence could the silicate of alumina be derived ? A superficial layer not altogether dissimilar, might, as suggested, be formed so long as the plants had access to subjacent rocks. Once, however, removed from contact with them, these inorganic elements of the plants could only be supplied from the soil itself. Rivers are inadmissible, as their action would have been to disintegrate, not to build up ; springs, from the peculiarities of the. formation, cannot rise to its surface. There is, finally, no known means by which these inorganic matters could have been supplied from the atmo-