172 



PHYSICAL GEOLOGY 



to the southern confines of Ohio, and when traced northward are seen 

 to have been derived from a deposit on the north shore of Georgian 

 Bay in Canada. Native copper from the copper deposits of Lake 

 Superior has been found in the drift many miles to the south. Pieces 

 of copper transported in this way were often picked from the drift 



and made into ornaments by the ancient 

 mound builders. In New England trains 

 of bowlders have often been traced to 

 outcrops which have some distinctive 

 character (Fig. 154). In any one deposit 

 the number of kinds of rock is usually 

 not very great, although in some cases 

 one may find as many as twenty different 

 varieties in a single bed of till. The 

 bowlders are often angular and scratched, 

 and in both of these features differ from 

 stones which have been rolled about by 

 streams. It should not be inferred from 

 the above that no rounded and un- 

 scratched bowlders occur in glacial debris, 

 for sometimes the angular and scratched 

 bowlders are in the minority. 



(2) Unstratified Drift. — As has been 

 said in connection with mountain glaciers, 

 all of the debris transported by the ice is 

 included under the general term drift; till 

 or bowlder clay being the unstratified 

 , drift, and that carried and later deposited 

 "bowlder train" from Iron Hill, by streams being called stratified drift 

 The direction ( p jyg) Till (Fig. 1 55) is composed of 

 a heterogeneous mixture of bowlders of 

 many sizes embedded in clay. The mix- 

 ture of coarse and fine material and the lack of stratification proves 

 without question that such deposits were not made by streams. 

 The stratified drift (Fig. 156) was deposited by melting waters 

 under various conditions. Drift is not confined to the valleys of 

 glaciated regions but is spread over hills as well, being in a measure 

 independent of topography. 



1 he deposition of drift may render a region either rougher (Fig 157) 

 or smoother (Fig. 1 58). If, for example, in passing over a region some- 



of the movement of the ice is 

 generalized. (After Hobbs.) 



