Page:Popular Science Monthly Volume 35.djvu/425

Rh hollows over a strip of ground nearly a mile in width, forms a continuous line of drift-hills (more or less marked) extending completely across the State. These hills vary in height from a few feet up to one hundred or two hundred feet, and, while in some places they are marked merely by an unusual collection of large transported bowlders, at other places an immense accumulation forms a noteworthy feature of the landscape. When typically developed this accumulation is characterized by peculiar contours of its own—a series of hummocks, or low, conical hills, alternate short, straight ridges, and inclosed shallow basin-shaped depressions, which, like inverted hummocks in shape, are known as kettle-holes. Large bowlders are scattered over the surface, and the unstratified till which composes the deposit is filled with glacier-scratched bowlders and fragments of all sizes and shapes.'

"From its lowest point in Pennsylvania, where it crosses the Delaware, 250 feet above the sea-level, this terminal moraine extends indiscriminately across hills, mountains, and valleys, rising over 2,000 feet above the sea in crossing the Alleghanies, and attaining the maximum of 2,580 feet on the high table-land farther west, being there 'finely shown at an elevation higher than anywhere else in the United States.'

"Preliminary outlines of Prof. Lewis's work on the glacial drift of England, Wales, and Ireland are given by his papers in the reports of the British Association for 1886 and 1887; and the first of these also appeared in the 'American Naturalist' for November, and the 'American Journal of Science' for December, 1886. Their most important new contribution to knowledge consists in the recognition of the terminal moraines formed by the British ice-sheet, which Lewis traced across southern Ireland from Tralee on the west to the Wicklow Mountains and Bray Head, southeast of Dublin; through the western, southern, and southeastern portions of Wales; northward by Manchester and along the Pennine chain to the southeast edge of Westmoreland; thence southeast to York, and again northward nearly to the mouth of the Tees; and thence southeastward along the high coast of the North Sea to Flamborough Head and the mouth of the Humber. It is a just cause for national pride that two geologists of the United States—Lewis in Great Britain in 1886, and Salisbury the next year in Germany—have been the first to discover the terminal moraines of the ice-sheets of Europe. Like the great moraines of the interior of the United States, those of both England and Germany lie far north of the southern limit of the drift.

"Another very important announcement by Prof. Lewis relates to the marine shells, mostly in fragments and often worn and