58 THE JOURNAL OF GEOLOGY. 



3. The boulders of this series are much more angular than 

 those of the typical till sheets. Some of them, indeed, are 

 rounded, but the rounding is generally of the type which bould- 

 ers derived by surface degradation and exfoliation present- 

 They rarely have the forms that are distinctively glacial.' Quite 

 a large percentage are notably angular, and have neither suffered 

 glacial rounding nor spherical exfoliation. Some few are gla- 

 cially worn and scratched, but the percentage of these is 

 small. 



The tracts therefore present these four salient characteris- 

 tics : ( I ) the boulders are derived from distant crystalline 

 terranes (400 to 500 miles) and are essentially uncommingled 

 with rock from the intervening paleozoic terranes ; (2) they are 

 essentially superficial, and the associated earthy material has a 

 texture differing from that of the subglacial tills ; (3) they are 

 notably angular and free from glacial abrasion, except in minor 

 degree ; (4) the tracts are so associated with terminal moraines 

 and so related to the topography of the region, that there is no 

 rational ground for doubt that the boulders were borne to their 

 present places by the glaciers that produced the correlative 

 moraines. 



In contrast to these superficial boulder formations, the till 

 sheets below are made up of a very large percentage of glacial 

 clay whose constitution shows that it was produced in part by 

 the grinding down of the paleozoic series. In this are imbedded 

 boulders and pebbles that were derived from the paleozoic series 

 as indicated by their petrological character, and, in many 

 instances, demonstrated by contained fossils. While a small 

 part of the boulders contained in the till are angular or but 

 slightly worn, the larger part are blunted, bruised, scratched and 

 polished by typical glacial action. This obvious grinding of the 

 boulders, taken in connection with the clay product resulting 

 from the grinding, affords a clear demonstration that the deposit 

 was produced at the base of the ice by its pushing, dragging, 

 rolling action. 



The two formations, therefore, stand in sharp contrast; the 



