S28 Geology of the Great Lakes and the Mississippi. 



SOU& from Lake Mdcliigaix— filled with clay, sand, trunks of trees, 

 etc. — which has been penetrated in one place to a depth of 230 feet. 

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

 enabled Professor Newberry not only to demonstrate the existence of 

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

 out. He points out the importance of a knowledge of these old 

 channels in the improvement of the navigation of our larger rivers, 

 as this may in many cases prove valuable in constnicting canals, 

 when millions of dollars might be expended in rock excavation. 



Upon the glaciated surfaces of the solid rocks are found a series 

 pf unconsolidated materials, generally stratified. These are the 

 Drift deposits, which occur in the following (ascending) order ;: — 

 i 1. The Erie clays of Sir W. E. Logan. They consist of blue aaid 

 red clays, finely stratified, with drifted coniferous wood and leaves, 

 ?ind containing in some places beds of gravel and boulders. In 

 Ohio these clays are nearly 200 feet in thickness. They fill the old 

 channel which formerly oonneeted laikes Erie and Huron ; here they 

 are over 200 feet thick. 



, 2. Above the Erie clays are Sands of variable thickness, less 

 widely spread than the clays. They contain beds of gravel, and 

 near the surface water-worn teeth of Elephants have been found, i 



3. Upon these clays, sands, and gravels, are scattered boulders of 

 all sizes, composed of granite, diorite, and dolerite, mica-slate, etc., 

 generally traceable to the Eozoic area north of the lakes. There are 

 also many balls of native copper from the copper district of Lake 

 Superior. 



■ Above all these Drifts, and more recent than any of them, are 

 "lake-ridges," embankments of sand, gravel, sticks, leavQs, etc., 

 which run rudely parallel to the present margin ^of the lakes, when 

 highlands lie in the rear. The author regards them as tru^ lake- 

 beaches. 



Professor Newberry gives some theoretical deductions regarding 

 the history of these deposits, and then discusses the origin of the Grreat 

 Lakes. Some of them are embraced in the folding of the Eozoic rocks^ 

 and fill synclinal troughs ; but most of the series, from Great Bear 

 Lake to Lake Ontario, are basins of excavation in the Palaeozoic 

 plain that flanks in a parallel belt the Laurentian area. The 

 bottoms and sides of the lake-basins, wherever exposed to observa- 

 tion, if composed of resistant materials, bear indisputable evidence 

 of ice-action, proving that these basins were filled by moving 

 glaciers in the last ice-period. He considers that no other agent 

 than glacial ice is capable of excavating broad, deep, boat-shaped 

 ba,sins, like those which hold the lakes. This theory, it is hardly 

 necessary to say, is in accordance with that which was first pro- 

 jnulgated by Professor Ramsay, and which, although it met with 

 disfavour when it was first started some time since (1862), has 

 certainly been gaining, ground, though -slowly, and it seems probable 

 that the glacial origin of rock-basins occupied by lakes will ere 

 Jong be generally accepted. — H. B. W. ■ : 



