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NEW YORK STATE MUSEUM 



barrier so as to occupy the northern third of the valley trough 

 from the mouth of the Mohawk to Montreal. Beyond the latter 

 point to Quebec both the Black river and Trenton deposits were 

 probably confined to the area covered by the former Chazy bay. 

 Trenton trans- Between the two Trenton transgressions the Normans kill shale 



gressions 



eastward intervened, its western edge overlapping the first and being in 

 turn covered by the second. The latter eastward transgression 

 of the Trenton is indicated chiefly by the fauna of the calcareous 

 shale overlying the Normans kill. A careful study of Mr Ruede- 

 mann's list of this fauna reveals nothing incompatible with a 

 late Trenton correlation. 



Immediately succeeding the Chazy, there is reason to believe, 



Ottawa bay a fold was developed across the mouth of the Ottawa 

 bay that has since been worn down to Upper Cambrio 

 rocks. This 1 fold must have been higher than the land formerly 

 bounding the western end of the bay and separated a new 

 Ottawa bay now coming in from the west, probably by way of 

 Lake Nipissing, from the narrow Champlain-Quebec basin. This 

 separation is indicated by both structural and paleontologic 

 evidence. 



At the close of the Trenton the Cincinnati axis or parma 

 experienced one of its periodic uplifts, and with it much of 

 the area west of it was raised above sea level. The region to 

 the east of it and north of the Ohio river, on the contrary, seems 

 to have been slightly depressed. Apparently the subsidence 



utica invasion was greatest in the Mohawk valley and in the Levis 

 basin of the Appalachian valley trough, and sufficient to 

 render the Quebec barrier wholly ineffective here. The north- 

 east communication with the Atlantic, now considerably 

 enlarged by the subsidence, brought in with the decided south- 

 west current, ingeniously demonstrated by Ruedemann, 1 a fauna 

 wholly new to the Mississippian sea, having, as has been 

 already asserted by Matthew and more recently by Ruedemann, 2 

 strong European affinities. 



1 Am. geol. 1897. 19 :367-91 ; 1898. 21:75-81. 

 2 N. Y. state mus. Bui. 42. 1901. p. 562. 



