64G 



NEW YOllK STATE MUSEUM 



Richmond 

 submergence 



Taconic 

 revolution 



compaiiifd by a submergence, the older taking: place, afi we have 

 described, in the region of the middle third of the Appalachian 

 valley, the later one in the west, where the preceding Lorraine 

 land was again submerged. 



The Richmond submergence is of great importance in the geo- 

 logic history of the North American continent, fossil evidence 

 bearing on the point indicating open communication of the entire 

 Mississippian sea, then existing, with Anticosti and northern 

 Europe. But as this communication was certainly not by way 

 of the St Lawrence-Champlain valley, and the problem therefore 

 is not intimately connected with the subjects of this paper, its 

 discussion is deferred. 



Toward the close of Ordovicic time the lands and seas, as 

 evidenced by the two Lorraine and Richmond emergence* 

 and submergences described, had become unstable. Now 

 followed one of the greatest earth pulsations in North 

 American Paleozoic history. The disturbance referred to, 

 Dana^ says gave birth to the Taconic mountains; and we will 

 therefore call it the Taconic revolution. That this movement 

 was one not only of elevation but also of considerable folding 

 of the earth's crust, is shown in the fact that the Helderbergian 

 deposits overlie unconformably the Ordovicic strata, as at 

 Becraft mountain. New York. That its effects were extensive 

 is indicated by Dana's remark, " The Taconic . . . series of 

 upturnings appear ... to extend all the way from the St Law- 

 rence valley to New York city." 



This revolution affected all North America, and there was 

 land perhaps throughout from Richmond to Oneida time. The 

 length of this land interval we can not perhaps now ascertain 

 satisfactorily, because there are no Mississippi sea deposits by 

 which its duration may be measured. In Minnesota, and more 

 particularly in Manitoba, there are late Ordovicic deposits with 

 prophetic Siluric genera and species which apparently indicate 

 that the land interval was not of long duration. "After a moun- 

 tain birth," says Dana,^ ** there has commonly succeeded a time 



» Manual of geology. Ed. 4. 189G. 

 •Manual of geology. Ed. 4. 1896. 



p. 38G and 531. 

 p. 386. 



