The deposition of marine gravels is examined from the points of view of the places of deposition, the depths of water, and the relation of the sites of deposition to sea-level. In connection with the problem an inquiry is made with respect to the possible thicknesses and extents of marine gravels and the possibilities of transportation of gravels into deep water.

An examination is made of the conditions that control in the development of unconformities beneath marine deposits and it is pointed out that unconformities may readily develop under submarine conditions. Some criteria for the determination of unconformities that develop beneath the sea are presented.

Lastly, there are considered the factors upon which thicknesses of deposits, particularly marine deposits, depend, and it is shown that under some conditions a given stratigraphic unit may range from zero to many hundreds and even thousands of feet. It is concluded that measurements of time based on thickness of deposits have little value.