252 ANNUAL OF SCIENTIFIC DISCOVERY. 



NOTES ON THE SURFACE GEOLOGY OF 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 alter- 

 ations 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 fol- 

 lowed 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 rocJics 

 moutonne's of the granitic islands in the St. Mary's River and Lake 

 Huron ; by all the hard, rocky margins of Lake Huron and Lake 

 Michigan ; by nearly all the surface rocks, when hard enough to 

 retain glacial furrows, of Ohio, Indiana, Illinois, Iowa, Wisconsin, 

 etc. 



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

 First, A series of blue laminated clays in horizontal beds, contain- 

 ing 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. Second, Yellow clays, sands, gravel, and boulders. Among 

 the latter are granite, trap, azoic slates, silurian fossiliferous limestone, 

 masses of native copper, etc., 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 

 limestones, often many tons in weight, are now scattered over the 

 surface of the slopes of the highlands of Ohio ; and, in some places, 

 collections of them are seen occupying areas of several acres, and 

 numbering many thousands, all apparently having been brought here 

 together and from one locality. 



(4) At various points are found remarkable pits, conical depres- 

 sions in the superficial deposits, which have been attributed to ice- 

 bergs stranding and melting, dropping their loads of gravel and stone 

 around their resting-places. 



(5) The beds of clay and other transported materials mentioned 

 above are several hundred feet in thickness, extending from at least 

 one hundred feet below the present water level in the lakes to points 

 five hundred feet or more above that level. 



(6) During the "glacial period" to which I have referred, the 

 whole country must have been relatively higher than at present, and 

 the drainage much more free ; for, during this epoch, the valleys of 



