Page:Popular Science Monthly Volume 68.djvu/305

wide dispersion of drift boulders over the northern part of the country, although the glacial character of the same was not dreamed of.

The paper, so far as existing literature shows, caused little discussion, and we have next to refer to observations by Dr. Samuel Akerly, who, in 1810, published in Bruce's American Mineralogical Journal a geological account of Dutchess County, New York. After referring to the Highlands and the country to the northward, he described the southern part—that upon which the then existing city was built—as composed of an alluvion of sand, stone and rocks. This he looked upon as a recent deposit, 'subsequent to the creation and even the deluge.' The manner in which this material was deposited he described in the following language:

After the waters of the deluge had retired from this continent, they left a vast chain of lakes, some of which are still confined within their rocky barriers. Others have since broken their bounds and united with the ocean. The Highlands of New York was the southern boundary of a huge collection of water, which was confined on the west by the Shawangunk and Catskill mountains. The hills on the east of the Hudson confined it there. When the hills were cleft and the mountains torn asunder, the water found vent and overflowed the country to the south. The earth, sand, stones and rocks brought down by this torrent were deposited in various places, as on this island, Long Island, Staten Island and the Jerseys. This opinion, he added, is mostly hypothetical, because unsupported by a sufficient number of facts.

A candid acknowledgment upon which the author is to be congratulated!

"Whose was the master mind that first conceived of this great barrier which held back the flood of waters, so long made responsible for the drift, I have not been able to ascertain. The theory is, however, given in greatest detail by Dr. Samuel L. Mitchill in his 'Observations on the Geology of North America,' published in 1818.

It was Mitchill's idea that the Great Lakes are the shrunken representatives of great internal seas of salt water, which ultimately broke through their barriers, the remains of which he thought to be still evident. One of them he wrote, seemed to have circumscribed the waters of the original Lake Ontario and to be still traceable as a mountainous ridge beyond the St. Lawrence in upper Canada, passing thence into New York, where it formed the divide between the present lake and the St. Lawrence and continued to the north end of Lake George, apparently crossing the Hudson above Hadley Falls. Thence, he believed it to run toward the eastern sources of the Susquehanna, which it crossed to the north of Harrisburg, and continued in a southeasterly direction until it entered Maryland, passing the Potomac at Harpers Ferry into Virginia, where it became confounded with the Allegheny Mountains.

To appreciate Mitchill's views, then, we have to imagine this now broken and gapped ridge as continuous. A time came, however, when at various points it gave way, the pent-up waters rushing through and