42 



Prof. W. B. Rogers read the following pajDer in behalf of 

 tlie author : — 



Notes on the surface Geology op the Basin of the Great 

 Lakes. By Dr. J. S. Newberry. 



The changes which have taken place in the physical geography of 

 the country surrounding the great Lakes, geologically speaking, with- 

 in a recent period, have been very great ; how great, and dependent 

 upon what causes, we cannot as yet definitely state, as much more 

 study than has hitherto been given to the subject will be necessary 

 before all its difficulties and obscurities shall be removed. 



These changes to which I have referred apparently include (a) 

 great alterations in the level of the water-surface in the lake basin, 

 and (b) in the elevation of this portion of the continent as compared 

 with the sea-level, with (c) corresponding alternations of temperature, 

 all followed by their natural sequences. 



The facts which lead to these conclusions are briefly as follows : — 



(1) The surfaces of the rocks underlying all portions of the basin 

 of the great lakes, except where affected by recent atmospheric action, 

 are planed down, polished, scratched, and furrowed, precisely as those 

 are which have been observed beneath heavy sheets and masses of 

 moving ice. 



The effect of this action is strikingly exhibited in the hard trap 

 ledges of the shores of Lake Superior ; by the roches moutonnes of the 

 sranitic islands in the St. Mary's River and Lake Huron ; by all the 

 hard, rocky margins of Lake Huron and Lake Michigan ; by the De- 

 vonian limestones underlying the surface deposits of the peninsulas of 

 Canada West and Michigan ; by the planed and grooved sui'faces of 

 the Coniferous limestone beneath the west end of Lake Erie, and com- 

 posing the group of islands off Sandusky ; by nearly all the surface 

 rocks, when hard enough to I'etain glacial furrows, of Ohio, Indiana, 

 Illinois, Iowa, Wisconsin, &c. 



(2) Upon these grooved and polished surfaces we find resting, — 

 First, A series of blue laminated days in horizontal beds, containing 



few shells, as far as yet observed, but, in abundance, water-worn 

 trunks of coniferous trees with leaves of fir and cedar, and cones of a 

 pine (apparently Abies balsamea, Juniperus Virginiana, and Pinus 

 strobus). 



Second, Yellow clays, sands, gravel, and boidders. Among the latter 

 are granite, trap, azoic slates, silurian fossiliferous limestone, masses 

 of native copper, &c., all of northern origin, and generally traceable 

 to points several hundred miles distant from where they are found. 



(3) Millions of these granite boulders and masses of fossiliferous 

 limestone, often many tons in weight, are now scattered over the sur- 



