336 Tertiary. 



the Laurentian mountains, and it is not improbable tliat eartliquakes 

 and volcanic energies had something to do with the emptying of these 

 vast bodies of water over the conntr\' to the south. The drift deposits, 

 to the west of Lake Superior, which spread over part of Minnesota, 

 and extend as far south as the Missouri river, belong to an overflow 

 of the great central lake of British America, which is evidenced b}' 

 the terraces and beaches of that extensive region. The overflows have, 

 therefore, not only occurred at difi'erent periods of time, but, probabl}'^, 

 from three different bodies of water. If then, all the phenomena are to be 

 accounted for by ordinary and well known forces of nature, why call to 

 their aid a glacial period, which will account for none of them. 



Taking a broad and general view, we would say that the drift 

 upon the eastern part of the continent, from the mouth of the Hudson 

 river to Hudson ba^^ is marine, and the striae upon the rocks were 

 produced under water. The age dates back to the Pliocene era, and 

 probabl}^ to the Miocene. When this margin was depressed, a corre- 

 sponding elevation took place east of Lake Ontario, that blocked up 

 the great river that had drained the central part of the continent, as 

 far west as Lake Superior, during the Triassic, Jurassic, Cretaceous 

 and earlier Tertiar}' periods. This elevation was more than 500 feet, as 

 proven b}^ the lacustrine clays exceeding that height, which were 

 formed upon the hill and mountain ranges surrounding the great 

 internal lake caused by this back-water, and as further evidenced by 

 the fact, that after the lake had been permitted to stand at this height 

 for so long a period as to form terraces and beaches, that later, it 

 excavated the elevated barrier to a depth of 500 feet, forming a chan- 

 nel, which is now in the bed of Lake Ontario, and when the eastern 

 coast was again elevated, this region was corresponding!}' depressed. 



The drift on other parts of the continent is fresh water or lake drift, 

 and the striae were produced, except in cases of drifting sand under 

 atmospheric influences, by the action of water forcing harder materials 

 against obstructions, or over barriers, and by floating shore ice having 

 frozen within it, the sand, gravel and bowlders of the place in which it was 

 formed. In the Rocky mountain region, each valley is the limit of its own 

 drift phenomena; but when the northern part of the range was elevated, a 

 very large interior lake was formed in British America, which seems 

 to have covered many vallej's, and in times comparatively recent, to 

 have overflowed the country so as to empty itself in part, into the 

 streams that flow south into the Missouri and Mississippi rivers. 



Anpther great overflow took place from the more central lake. This 



