{ _Subaqueous_ Conglomerate, sandstone { Deposited by water. and shale. { _Subaërial_ or _Eolian_ Sandstone and loess. _Mechanical_ { Deposited by wind. { _Glacial_ Till and tillite. { Deposited by ice. { _Fluvio-glacial_ Sands and gravels. { Glacier-water deposits.
{ Calcareous tufa Deposited in springs { and rivers. _Chemical_ { Oölitic limestone Deposited at the { mouths of rivers { between high and { low tide.
{ Formed of plant remains. Peats and coals. _Organic_ { Formed of animal remains. Limestones and { marls.
Winds are under favorable conditions capable of transporting both dust and sand, but not the larger rock fragments. The dust deposits are found accumulating outside the borders of deserts as the so-called _loess_ (Fig. 216), though the sand is never carried beyond the desert border, near which it collects in wide belts of ridges described as dunes. When this sand has been cemented into a coherent mass, it is known as eolian sandstone. A section of the appendix (B) is devoted to an outline description of some of the commoner rock types.
=The different deposits of ocean, lake, and river.=—Of the subaqueous sediments, there are three distinct types resulting: (1) from sedimentation in rivers, the _fluviatile_ deposits; (2) from sedimentation in lakes, the _lacustrine_ deposits; and (3) from sedimentation in the ocean, _marine_ deposits. Again, the widest range of character is displayed by the deposits which are laid down in the different parts of the course of a stream. Near the source of a river, coarse river gravels may be found; in the middle course the finer silts; and in the mouth or delta region, where the deposits enter the sea or a lake, there is found an assortment of silts and clays. Except within the delta region, where the area of deposition begins to broaden, the deposits of rivers are stretched out in long and relatively narrow zones, and are so distinguished from the far more important lacustrine and marine deposits.
Lakes and oceans have this in common that both are bodies of standing as contrasted with flowing water; and both are subject to the periodical rhythmic motions and alongshore currents due to the waves raised by the wind. About their margins, the deposits of lake and ocean are thus in large part wrested by the waves from the neighboring land. Their distribution is always such that the coarsest materials are laid down nearest to the shore, and the deposits become ever finer in the direction of deeper water. Relatively far from shore may be found the finest sands and muds or calcareous deposits, while near the shore are sands, and, finally, along the beach, beds of beach pebbles or shingle. When cemented into coherent rocks, these deposits become shales or limestones, sandstones, and conglomerates, respectively.