528 



CENOZOIC TIME. 



2. General Geographical Distribution of the Drift. — The unstrati- 

 fied Drift in North America occurs from Canada and Labrador north- 

 ward, and west to a northwesterly line passing not far west of Lake 

 Winnipeg; over New England and the islands south ; New York, New 

 Jersey, and part of Pennsylvania ; the States west, including Iowa 

 and Minnesota, to the meridian of 98° W., and not beyond. 



It has its southern limit near the parallel of 39°, in southern Penn- 

 sylvania, Ohio, Indiana, Illinois, and Kansas ; but its northern is unde- 

 termined. South of the Ohio River, it is hardly traceable ; yet it is 

 stated to occur near Ashland, in Boyd County, Kentucky. Few bowl- 

 ders are found about Baltimore and Philadelphia, and these not od 

 the higher lands. It is thus northern in its distribution. Still, local 

 Drift deposits have been recognized,descending from the Unaka Moun- 

 tains (the range between Tennessee and North Carolina), along tribu- 

 taries of the Tennessee River, and in the Alleghany Mountains, West 

 Virginia ; and of far greater extent about the crest ranges of the Rocky 

 Mountains, the Sierra Nevada, down to latitude 35° N., the peaks of 

 the Cascade Mountains, and other high ranges on the Pacific Border. 



In East Tennessee, the stones of the Drift are of all sizes, to a diameter of eight or ten 

 inches, and the trains have a height of 300 to 400 feet above the streams, in their upper 

 portions, according to Safford, and of 170 feet at Knoxville, according to F. H. Bradley. 

 E. P. Stevens has announced the occurrence of similar " bowlder Drift," in Greenbrier 

 valley, AVest Virginia, on the west slope of the Alleghanies, and also near Covington, 

 Va., along the head waters of the James, on the opposite or east side. The trains arc 

 valley trains, not continental and northern, like the true Drift. In the Rocky Moun- 

 tains, and in Nevada, California, and Oregon, there is no northern Drift, according to 

 Whitney; but there are unstratified and stratified Drift deposits of great thickness, 

 following the course of the valleys from the higher mountains. Belt states that there 

 are bowlder-clays in Nicaragua, 2,000 to 3,000 feet above the sea. 



The closing Tertiary age must have left the continent covered with 

 alluvial and lacustrine deposits, and among them beds of peat, and 

 shell -beds of fresh- water origin. The preceding pages contain an 

 account of such deposits over the Rocky Mountain slopes. But little 

 is known of any such beds, north of the Drift limit, east of the Mis- 

 sissippi : they appear to have been mostly rearranged, in the making 

 of the Drift. The whole country must have been a vast forest region. 

 The forests were all swept off; for existing forests over the hills are 

 planted in general upon the Drift deposits, or on material of later for- 

 mation. 



Distribution in Elevation. — The unstratified Drift extends not only 

 over the lower country, but also high up the mountains ; to a level of 

 5,800 feet on the north side of Mt. Washington, and 4,400 feet on Mt. 

 Mansfield, the highest peak of the Green Mountains. Bowlders, often 

 of large size, occur on most of the New England summits under 

 4,000 feet in height. 



