64 SURFACE GEOLOGY. 



contemporaneous with all other periods ; or rather, each period had its alluvium, 

 and sometimes the same alluvium may have belonged to successive periods. These 

 facts give a peculiarity to the alluvial formation possessed by no other. 



32. It appears that the time since man came upon the globe, has been only a 

 small part of the alluvial period. For we find none of his remains, nor works, 

 except in the superficial portions of the terraces. The lowest of these, save alluvial 

 meadows, are often the seat of his most ancient works — his habitations and forts. 

 The remotest epochs of history rarely, if ever, reach back to the time when the 

 most recent terrace, save overflowed meadows, was formed. Even if it be admitted, 

 which yet requires proof, that his remains are found with those of extinct animals, 

 this by no means throws back his origin, as has been supposed, to what is usually 

 understood by the drift period, for many races of animals have disappeared since 

 alluvial agencies have been at work. 



33. A large proportion of those superficial deposits in high latitudes, that have 

 been usually included in drift, appear from the views that have been presented, to 

 have been the work of agencies greatly posterior ; analogous probably to those 

 that produced the lowest and coarsest drift, but still greatly modified. These 

 agencies have taken the drift and worked it over, and though the same kind of 

 drift as the oldest is still produced in some parts of the globe, yet it is undesirable 

 to confound modified with unmodified drift, since it embarrasses our reasonings as 

 to the origin of that coarse deposit which usually lies beneath all others that are un- 

 consolidated, and which all geologists agree in regarding as drift. The super- 

 imposed beds of gravel, sand and clay, demand only water to explain their origin ; 

 whereas all geologists at this day would agree that the coarse drift must have been 

 the result, in part at least, of glacial action. Besides to blend drift proper and 

 modified drift is almost as much of an anachronism as to regard the conglomerates 

 of the triassic or carboniferous period^ as contemporaneous with the fragments of 

 which they are composed. 



34. But after all, the idea so long and generally maintained, that the drift 

 agency operated for a certain length of time after the tertiary epoch, and then 

 ceased, and was succeeded by alluvial action, which did not operate during the 

 drift period, I find myself compelled to abandon. For T find evidence that both 

 these agencies have been in parallel operation from the close of the tertiary epoch, 

 to say nothing of earlier periods. They have varied only in the amount of their 

 action. During the earlier part of the period, drift agency largely predominated, 

 as the alluvial agency has since done. Hence the attempt to fix upon a certain 

 definite time when drift agency ceased and alluvial agency commenced, has so 

 signally failed, and scarcely no two geologists have drawn the line in the same 

 place. But I shall recur to this point again after laving down a few more posi- 

 tions. 



35. It appears that the organic remains which have been referred to the drift, 

 do, in fact, belong to modified drift, and generally to a very late stage of the allu- 

 vial period. The marine remains are the oldest, such as are found on the shores 

 of Lake Champlain, and on the banks of the St. Lawrence, at Montreal; on Long 

 Island, at Brooklyn ; at Portsmouth, New Hampshire, and at Portland and other 



