REPORT OP THE STATE PALEONTOLOGIST 1901 659 



Summary and general conclusions 



Permanence of land masses and of folds of the earth's crust. Our 

 studies tend to the conclusion that the present North American 

 continent was in existence, and practically in full development as 

 land, at the close of Algonkian time and that since that period, 

 the Canadian shield and other smaller Archean land areas have 

 never been wholly submerged. The periodic encroachment of 

 the sea on the Canadian shield attained considerable extent on 

 the north and west and more particularly on the south. The 

 east shore, on the contrary, remained nearly the same till com- 

 paratively recent time— probably Postcretaceous. 



The present main lines of elevation of the continent were in 

 existence in Algonkian time and have been maintained without 

 serious modification to the present day. Concerning the anti- 

 clinal folds that began in Paleozoic and later times, we think 

 that all known evidence bearing on the point goes to prove that, 

 following their inception, they, in common with those of older 

 date, were never changed except 1) to be periodically accentu- 

 ated, 2) to have their axes migrate slightly landward, like the 

 summit of a wave, in correspondence with effects of active com- 

 pression and subsequent gravitational adjustments, and 3) to 

 be modified in their relations to the general plan of crustal 

 folding by the development of folds of subsequent origin. 



We agree with Walcott's conclusion that in Lower Cambric 

 time the greater part of the interior of the continent was land, 

 and that the first Paleozoic subsidence of the interior and the 

 real birth of the Mississippian sea occurred with what we term 

 the St Croix invasion. 



Bhythmic pulsations. There is a rhythmic relation between 

 the successive grand subsidences and emergences of the interior 

 of the continent that we believe should be the basis of a revised 

 classification of the rocks of North America. Such relation was 

 indicated by Amos Eaton and later by Newberry and others. 

 Each system should begin with a subsidence and end with an 

 emergence. While such a classification will be in some respects 

 different from the one now in use, and its adoption therefore 



