melting or grounding on muddy bottoms of the iceberg masses floated off from the end of such a glacier. It is altogether likely, from the observations recently made in Greenland, that in that country such a deposit is being formed in all these ways. In like manner, the ancient boulder clay may have been formed in one or more of these ways in any given locality where it occurs, though it may be difficult in many instances to indicate the precise mode. There are, however, certain criteria which may be applied to the determination of its origin, and I may state a few of these, which are the results of my own experience. (1) Where the boulder clay contains marine shells, or rounded stones which if exposed to the air would have been cracked to pieces, decomposed, or oxidized, it must have been formed under water. Where the conditions are the reverse of these, it may have been formed on land. (2) When the striations and transport of materials do not conform to the levels of the country, and take that direction, usually N.E. and S.W., which the Arctic current would take if the country were submerged, the probability is that it was deposited in the sea. Where, however, the striation and transport take the course of existing valleys, more especially in hilly regions, the contrary may be inferred. (3) Where most of the material, more especially the large stones, has been carried to great distances from its original site, especially over plains or up slopes, it has probably been sea-borne. Where it is mostly local, local ice-action may be inferred. Other criteria may be stated, but these are sufficient for our present purpose. Their application in every special case I do not presume to make; but I am convinced that when applied to those regions in Eastern America with which I am familiar, they necessitate the conclusion that in the period of extreme refrigeration, the greater part of the land was under water, and such hills and mountains as remained were little Greenlands, covered with ice and sending down glaciers to the sea. In hilly and broken regions, therefore, and especially at considerable elevations, we find indications of _glacier_ action; on the great plains, on the contrary, the indications are those of _marine_ glaciation and transport. This last statement, I believe, applies to the mountains and plains of Europe and Asia as well as of America.