QUATERNARY AGE. GLACIAL PERIOD. 529 



3. Material of the Drift. — The unstratified Drift consists of (1) un- 

 stratified clay-beds, often with intermingled stones ; (2) the bowlder- 

 clay, already mentioned ; (3) sand, or (4) gravel, in great deposits ; 

 (5) bowlders, small or large, distributed in or over the other deposits, 

 — these bowlders sometimes twenty to thirty feet across, and weighing 

 500 to 1,200 tons. 



The material, though varying much in different regions, is in gen- 

 eral coarsest to the north, and becomes gravel and sand, without stones, 

 or only small ones, toward the southern limit of the Drift region. 

 Nearing this limit, it stretches farther south in the north-and-south 

 valleys than on the hills. 



The stones or bowlders sometimes lie in long trains, as in Richmond, 

 Berkshire County, Mass., and Huntington, Vt., crossing hills and val- 

 leys, without following the line of slope ; or going obliquely across a 

 valley ; or the stones of one ridge are found on another ridge sepa- 

 rated from it by a deep valley. 



One bowlder in Bradford, Mass., is 30 feet each way (Hitchcock), and weighs not less 

 than 1,250 tons. Another, in Whitingham, Vt., in the Green Mountains, is 43 feet 

 long and 32 in average width, and full 40,000 cubic feet in bulk. It lies on the top of a 

 naked ledge. Many on Cape Cod are 20 feet in diameter, and one at Winchester, N. 

 H., is 29 feet across. 



4. Soitrce of the Material, and Course of Travel. — By comparing the 

 stones of the Drift with the rocks of the surrounding region, it has 

 been found that the material has come, for the most part, from the 

 north, — either the northeast, or the north, or the northwest, — and in 

 most parts of the country from the northwest ; and it has been trans- 

 ported to a distance usually between a mile, or less, and fifty miles, but 

 sometimes one or more hundred miles. 



From southwestern Vermont, the granyte of a high hill, between Stamford and Pow- 

 nal, which is almost as high as the Green and Hoosac Mountains lying to the east and 

 southeast, has been carried southeastwardly across the western sides of these moun- 

 tains, nearly, across the State of Massachusetts. 



Large bowlders strew thickly the north shores of eastern Long Island, which are the 

 crystalline rocks, trap, and sandstone of New England; and others, on western Long 

 Island, are from the Palisades and heights along the Hudson River. South of Lake 

 Superior, there are bowlders which have come from the north shore of the lake. 



The iron-ore bed of Cumberland, Rhode Island, furnished bowlders for the country 

 south of Providence, thirty-rive miles distant, while none are found to the northward. 



South of the Lake Superior region (where native eopper occurs) masses of this metal 

 are found in the Drift, over Michigan, Ohio, Indiana, Illinois, Wisconsin, and Iowa: 

 and bowlders full of fossils, derived from various Paleozoic rocks of the upper Missis- 

 sippi, in the Drift of the States to the south, even down to Mississippi. The stones of 

 the Mississippi Drift have been traced in part to Tennessee. Masses of native copper 

 occur also in the Drift of Connecticut and New Jersey, that were taken from veins 

 nearly north of the places where the)'- occur. Native gold, from the rocks north of 

 Lake Superior, occurs in the Drift of Ohio, Indiana, and the States west. 



The Transportation was sometimes across, and sometimes in accord- 

 ance with, the slopes of the surface. — The facts stated above, respect- 



34 



