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as it must have been to account for the various observed phenomena—such phenomena as would necessitate the occurrence of water loaded with ice and detritus floating for centuries at least over a large part of the earth's surface.

His paper showed a very clear insight into what had taken place, but an inability, with the information at that time available, to account for it in a satisfactory manner. Thus, in describing the striae found by himself on the top of hills and mountains like Monadnoc, he wrote:

Could immense icebergs have been stranded on the northern slope of the hills and afterwards, by the force of currents, have been driven over the summits; or would it be necessary to suppose that, after the stranding, the water must have, risen so as to lift the iceberg; or would a vast sheet of ice lying upon the earth's surface, by mere expansion, without the presence of water, have been able to produce the smoothing and furrowing in question?

After considering the phenomena and weighing all the theories advanced from time to time by the authorities quoted, he summed up the matter in the following words:

Is it not possible that the phenomena of the drift may have resulted from all the causes advanced in the theories under consideration? I feel . . . that the proximate cause of the phenomena of drift has at last been determined, namely, the joint action of water and ice.

In 1836 there was organized a state geological survey of New York, which was placed in charge of W. W. Mather, Ebenezer Emmons, Lardner Vanuxem and James Hall—men whose names have since become too thoroughly identified with American geology to ever become eradicated. Naturally drift phenomena attracted the attention of these workers, and each expressed opinions, some of which may be referred to in detail.

Seventy-five pages of Mather's report, as published in 1843, were given up to descriptions and discussions of drift phenomena. He concluded that the transport of the material and the production of scratched surfaces were contemporaneous, the drift itself being transported in part by currents and in part by ice itself drifted by the currents. The period of the drift and that of the quaternary deposits were separated by a partial submergence of the land, and, further, the periods of the drift were periods when the currents were stronger than at the present time. He conceived this to be due to a collapse of the crust of the globe upon its nucleus, causing an acceleration of the velocity of rotation, and this causing, in its turn, a disturbance of the form of equilibrium of the spheroid of rotation which had been compensated by the flow from the polar regions and an accelerated flow to the equatorial regions. This sudden acceleration of the ocean currents he felt would be sufficient to cause the transportation of vast quantities of detritus-laden ice from the polar regions southward. The large amount of drift scattered over the central and northern Mississippi region he ascribed incidentally to ice-laden currents from