Page:Popular Science Monthly Volume 68.djvu/320

316 A ready explanation of the origin of this newest Pleistocene deposit (i. e., that of the Hudson and Lake Champlain districts) suggests itself when we consider the nature and energy of the crustal movements which lifted the Laurentian clays and sands to a height, in one locality at least, of not less than five hundred feet, and which drained wide tracts of the upper Laurentian Lakes.

The mere agitation or pulsating movement of the crust, if accompanied by any permanent uplift of the land, would suffice, we would think, by lashing the waters of the tidal estuaries in one quarter and the lakes in the other, to strew a portion of the older drift bordering all those basins in wide dispersion upon the top of the more tranquil sediments. But if such a pulsation of the crust were accompanied by successively paroxysmal liftings of wide tracts of the land, then the inundation would take the form of stupendous currents, the strewing power of which would be adequate to any amount of superficial transportation, even to the remote transportation of the larger erratics.

In 1861 the Natural History Survey of Maine was inaugurated and C. H. Hitchcock was placed in charge of that portion relating to geology. Of his work, only that relating to glaciers concerns us here. He noted that the fossiliferous marine clays which were regarded as of the same age as similar deposits along the St. Lawrence and Champlain valleys and referable to the terrace period, sometimes underlay a coarse deposit referable to the modified drift. Without committing himself definitely on this point, he suggested the possibility, therefore, of a recurrence of the drift agencies, that is, a period of second drift, as had the elder Hitchcock fifteen years earlier.

The drift period itself, according to Hitchcock's view as here expressed, was inaugurated by a depression of this portion of the continent amounting to at least 5,000 feet below that of to-day, and it was during this period of depression and reelevation that the drift deposits were formed through the joint agency of icebergs and glaciers.

In 1862 J. S. Newberry expressed his views on glaciers in an article on the 'Surface Geology of the Basins of the Great Lakes.' After reviewing the surface conditions as he saw them, he came to the conclusion that, at a period corresponding in climate, if not in time, with the glacial epoch of the old world, the lake region, in common with all the northern portion of the American continent, was raised several thousand feet above the level of the sea. This was to him the glacial period, during which the surface of the country was planed down and the deep fiords along the Atlantic coast formed. This was followed by a period -of depression, when all the basin of the Great Lakes was flooded with fresh water, forming a vast inland sea in which the laminated blue clays (the oldest drift deposits) were precipitated.

Subsequent to this deposit of blue clay an immense quantity of gravel and boulders was transported from the region north of the Great Lakes and scattered over a wide area south of them. This he regarded as due to floating ice and icebergs.

It would seem that, if one were looking for original observations on drift phenomena, he might turn with safety to the writings of the