184 Frank Carney 



The origin of Luke Erie 217 



Lakes in general 



The St. Lawrence drainage basin in i)i"eglacial times 



Local warping 



Glacial erosion 

 Old shore lines in Ohio 224 



Origin of shore lines 



The development of cliffs 



Beaches 



Along-shore currents 



Under-tow 



Bays 



Other shore line structure 



Geographic influences 



Post-glacial tilting 



INTRODUCTION 



In many of the northern states and much of Canada, one cannot 

 get away from the evidences of glaciation. It has been estimated 

 that the area of the continental glacier was 4,000,000 square miles. 

 No page in the geological chapter is plainer, yet students were very 

 slow in reading it correctly. Of all the evidence, the most striking, 

 perhaps, is the presence, in an area of organic and clastic rocks 

 only, of scattered bowlders of crystalline rocks. We sometimes 

 call these "erratics," sometimes "nigger heads." Early the ques- 

 tion was asked, how did they come here? But for a long time the 

 question w^as not correctly answered. Most students who gave 

 the matter any attention said that they were dropped from the 

 bottom of icebergs that floated about over the lands when covered 

 by floods, possibly the floods of Noah's deluge. Then other curi- 

 ous phenomena were noted : Broad rock surfaces were seen to be 

 striated and grooved. At first it was said that these markings 

 only showed where icebergs, shod with stones, had bumped along 

 across the shallow parts of the seas. But how could this make the 

 markings so parallel, it was asked, and why did the striae alwaj's 

 have such a uniform direction? These were indeed puzzling 

 questions, but not too severe for those of much orthodox}^ and 

 little reason. Again, men noted mounds of heterogeneous material, 

 large and small stones, stones of many varieties. These tumuli 

 were sometimes in the lower places, often on valley walls, and 

 sometimes on the highlands between valleys. Streams, it was 



