Great Lakes, and the YdUey of the Mississippi. 215 



dred feet. A few examples will suffice to show on what evi- 

 dence this assertion is based. 



Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario 

 are basins' excavated in undisturbed sedimentary rocks. ( M' 

 these. Lake Michigan is 600 feet deep, with a surface level oi 

 57S feet above tides; Lake Huron is 500 feet deep, with a sur- 

 face level of 574: feet; Lake Erie is 204 feet deep, with a sur- 

 face level of 565 feet ; Lake Ontario is 450 feet deep, with a 

 surface level of 234 feet above the sea. 



An old, excavated, now-filled channel connects Lake Erie 

 and Lake Huron. At Detroit the rock surface is 130 feel be- 

 low the city. In the oil region of Both well, &c, from .">n to 

 200 feet of clay overlie the rock. What the greatest depth of 

 this channel is, is not known. 



An excavated trough runs south from Lake Michigan — filled 

 with clay, sand, tree trunks, &c— penetrated at Bloomington, 

 111., to the depth of 230 feet. 



The rock bottoms of the troughs of the Mississippi and Mis- 

 souri, near their junction or below, have never been reached, 

 but they are many feet, perhaps some hundreds, beneath the 

 present stream-beds. 



The borings for oil in the valleys of the Western rivers have 

 enabled me not only to demonstrate the existence of deeply 

 buried channels of excavation, but in many cases to map them 

 out. Oil Creek flows from 75 to 100 feet above its old chan- 

 nel, and that channel had sometimes vertical and even over- 

 hanging cliffs. The Beaver, at the junction of the Mahoning 

 and Shenango, runs 150 feet above the bottom of its old 

 trough. 



The Ohio throughout its entire coarse runs in a valley which 

 has been cut nowhere less than L50fee1 below the preeen! river. 



The Cuyahoga enters Lake Erie at Cleveland, more than 

 loo feet above the rock bottom of its excavated trough. Tie' 

 Chagrin, Vermilion, and other streams running into Lake 

 Erie exhibit the same phenomena, and prove that the Burface 



