No. 4.] CLAYPOLE — PRE-GLACIAL GEOGRAPHY. 203 



opinions of Dr. Newberry as expressed in the volumes of the 

 Ohio Survey. It seems necessary, however, to dwell on this 

 point somewhat more fully in order to show that the theory of 

 the origin of our lake basins here maintained is more consonant 

 with facts than that which attributes it to the action of ice. Dr. 

 Newberry says (1876, p. 74) : 



" There can be no doubt that the basin of each of the great 

 lakes has been produced by a local glacier, and that the great 

 ice-sheet which existed during the period of intensest cold, 

 moving as a solid continuous mass of <>reat thickness from north 

 to south would have the effect to obliterate rather than to form 

 such local troughs. Our lake basins must therefore have been 

 formed before or after the continental glacier, or both before and 

 after. Probably the latter is the true statement of the case." 



The central and eastern portions of the bed of Lake Erie were 

 once occupied by soft rocks. Of these more than 1000 feet in 

 thickness were removed. To this enormou? erosion by the ice, 

 to which Dr. Newberry evidently ascribes the origin of the Erie 

 valley, the following passage from the same volume suggests a 

 serious objection : " An interesting fact was noticed by Mr. 

 Gilbert, Mr. Winchell and myself, that in the north-west portion 

 of the State, a series of glacial markings which have a nearly 

 north and south bearing are obliterated (nearly obliterated ?) by 

 the stronger, fresher, and more numerous grooves of which the 

 bearing is nearly east and west." 



The north and south grooves, to which Dr. Newberry here 

 refers, are of course those attributed to the continental ice-sheet, 

 while the east aud west grooves of later date are those caused 

 by the local glacier which followed it as the ice-sheet dwindled 

 away. We cannot agree, however, with Dr. Newberry's reading 

 of this natural palimpsest, for it appears highly improbable that 

 the excavation of the lake basin was principally effected by this 

 local east-west glacier, which was evidently unable to remove the 

 superficial scratches left by its larger predecessor. 



All will agree, we think, with Dr. Newberry that the effect of 

 the great ice sheet would be to obliterate rather than to form 

 such local troughs. But even this planing effect seems greatly 

 overrated. There is no proof that the great ice-sheet has re- 

 moved more than an inconsiderable layer of the superficial rock 

 of the region. Why then, we may ask, should a local glacier 

 be supposed able to excavate so deeply rocks on which the great 

 Vol. VIII. n No. 4 



