264 Prof. Rogers's Address before the 



their probable influence in dispersing bowlder matter, by Mr. Couthouy 

 and Mr. John L. Hayes. In addition to the valuable facts and views 

 thus imparted, the animated discussions at some of our meetings have 

 elicited from many of the gentlemen mentioned, and from others, much 

 impoi-tant information. 



To embark upon a full view of all that has been done of late in field 

 investigation and discussion connected with this multifarious subject, 

 would lead me quite beyond my limits, and I shall therefore content 

 myself with as brief a statement as possible of the chief generalizations 

 and theoretical conclusions to which the geologists of this country have 

 arrived. And here let me advert to the truly favorable field which 

 North America, with its wide expanse and its peculiar surface, affords 

 us, for testing some of the leading theories of drift now advocated in 

 Europe and this country. 



The most important facts connected with the great detrital stratum, 

 are of four classes ; those which relate to the grooves or scratches on 

 the rocky surface beneath the drift ; those which refer to the distribution 

 of the bowlder material ; those which indicate the condition of level of 

 the land at the period of the formation ; and those which imply the 

 epoch and duration of the action. The principal phenomena in relation 

 to the surface on which the drift rests are these. 



1st, The smoothed and furrowed surface is coextensive or nearly so 

 with the drift stratum, and it occurs at all altitudes, from the summits of 

 the loftiest mountains of New England and New York, to the beds of 

 the valleys, and over the whole broad plain of the lakes and the western 

 states. In the mountainous and hilly tracts, the northern and northwest- 

 ern brow and flank of each eminence, are much more smoothed and stri- 

 ated than the opposite. The scratches do not radiate from the high 

 mountain summits, but in the vast plains and prairies of the west, among 

 the confused hills of New England, or on the transverse mountain crests 

 of northern Pennsylvania, and western Vermont and Massachusetts, they 

 maintain invariably in all the higher levels a general southeasterly di- 

 rection. In lower situations, however, on the slopes of the great drain- 

 age valleys, their course is diverted to conform more nearly and some- 

 times with exact parallelism to the direction of the natural barriers and 

 channels. They exhibit a remarkable general parallelism among them- 

 selves, yet do we seldom meet with a striated surface of any extent 

 which does not disclose more than one set of furrows ; the more recent 

 and distinct crossing the fainter one at various small angles. Nor are 

 the scratches truly straight over any considerable length, except where 



