Ravm(i\i) : The Chazv Formation and its Fauna. 509 



Tlie Closing Period of Chazy Time. 



In the preceding pages an effort has been made to show that in 

 northeastern New York and southern Canada, the Chazy sea invaded 

 over a land surface of Beekmantown rocks, and that the base of the 

 Chazy is a tangential sandstone. 



Of the former extent of the formation there are {*t\v hints. Since 

 the sea did not attain the region of Aylmer until very late Chazy time, 

 it is probable that the formation never extended much west of the 

 known outcrops in that region (Allumette Island, etc.). 



From a study of the stratigraphy and faunas it becomes evident that 

 the upper portion of the Chazy is not represented in the region south 

 of Valcour Island. Either these beds were not deposited there, or 

 they were eroded before the Lowville limestone was laid down. The 

 evidence is not of such a character as to prove definitely which did 

 occur, but for reasons to be given it seems more probable that the 

 upper beds were deposited south of ^'alcour Island and later eroded. 

 These reasons are as follows : 



First. The sandstone immediately following the Chazy throughout 

 the Champlain Valley may be interpreted as the invading base of the 

 Lowville (Upper Stones River). From this it would follow that a 

 period of erosion existed between the Chazy and Lowville. 



Second. The other supposition is that the Chazy sea advanced 

 slowly to the south to some i)lace below Orwell, Vermont, and then 

 retreated to the northward. Such a retreat could have been caused 

 only by an elevation south of Orwell, as there is no general retreat 

 of the Chazy sea at this time, proven by the fact that at a still 

 later time the sea advances to the vicinity of Aylmer and Ottawa. 

 That there was no uplift at that time in the south is shown by the fact 

 that the Stones River invasion from the southwest comes first upon the 

 eroded Beekmantown and then over the various horizons of the Chazy 

 as it proceeds northward. The conclusion from these facts is that the 

 Chazy sea invaded southward to the region of Orwell, depositing here 

 the final ( Cainarotaschia piena) beds of the formation. The Chazy sea 

 then vanishes from the area of Lake Champlain, and while this is 

 going on, the Stones River sea invades from south to north. During 

 this time of Stones River advance and Chazy retreat, there was a 

 land interval, in which some of the Chazy and Beekmantown beds 

 were removed along the barrier region between Orwell and the 

 Mohawk \'allev. 



