The form of the deposits that are taking place on the sea-bottom at the present day is one of the essential elements required to be known when we wish to interpret the submarine contours, as throwing light on the submergence or elevation of the land in late geological times, or when we propose to use the variation of thickness of the strata deposited during any epoch as an indication of the position of the shore-lines at that time.

In the case of deposits in small or temporary masses of water, their form and arrangement may sometimes be observed directly; but in the case of the deposits in the sea, where we can neither remove the water nor make borings beneath it, we can only avail ourselves of theoretical considerations.

It might have been expected that the original form of various sedimentary deposits would have been considered in detail long ago, but as a matter of fact the few writers who have touched upon the question have mostly been content with the assumption that deposits taken as a whole are thickest near the source of supply, and the figures given in illustration of the arrangement of various kinds, and thereby the shape of each, are remarkable for their variety.

As the theoretical results at which I have arrived differ fundamentally from the ordinary assumptions, it is to be hoped that some one will be able to point out the fallacy, if any, which has led me astray, and to explain more satisfactorily the observed features which appear to confirm the theory.