P. F. Raymond — Fauna of the Chazy Limestone. 365 



First. All through the Champlain Valley, the Chazy is 

 capped by a bed of sandstone 2 feet in thickness, and this 

 may be interpreted as the invading base of the Lowville 

 formation. From this it would follow that a period of erosion 

 existed between the Chazy and Lowville formations. 



Second. If the upper beds were never deposited south of 

 Valcour, the Chazy sea after advancing slowly to the south to 

 some point below Orwell, Vermont, must have then retreated 

 to the northward. Such a recedence could have been caused 

 only b} T an elevation south of Orwell, for there is no general 

 retreat of the Chazj T sea at this time, which is proved by the 

 fact that at a still later period the sea advanced westward 

 beyond Ottawa. That there was then no uplift in the south is 

 shown by the fact that the Lowville sea invades from the south- 

 west.* On the other hypothesis, which seems more probable, 

 the sea would have invaded southward to the region of Orwell 

 and after depositing there the final, or Caniarotoschia plena, 

 beds vanished from the area of Lake Champlain. During the 

 latter part of Chazy time or after its close, the Stones River 

 (Lowville) sea was invading from south to north and there was 

 a land interval in the Champlain region, during which time 

 some of the Chazy and Beekmantown beds were removed 

 along the barrier region between Orwell and the Mohawk 

 Valley. 



Third. By taking the rate of decrease in thickness (11*25 

 feet per mile) of the Hebertella exfoliata division between 

 Chazy and Valcour Island, to compute the probable southern 

 extent of that division, it is seen that it would have reached 

 only 26'6 miles south from Valcour Island. Therefore, at the 

 same rate of decrease the base of the Crown Point section is 

 461 feet higher than the base of the Valcour Island section. 

 That this rate of decrease can not be used, is shown by the 

 fact, that Division 1 at Isle La Motte is only 225 feet thick, 

 which is less than at Valcour Island, while Isle La Motte is as 

 far north as is Chazy. The only reliable data for an estimate 

 of this character are the facts that there are 300 feet of the 

 beds of Division 1 at Valcour Island and nothing at Crown 

 Point. This is a thinning out of 7*3 feet per mile, which, on 

 the other hand, is probably too small. On this basis, the 

 bottom of the Crown Point section is at least 300 feet above 

 the base of the Valcour Island section and the base of the 

 Orwell section is at least 121 feet above it. If this minimum 

 estimate of the height of the base of the Crowm Point section 

 above that of the Valcour Island section is accepted as a work- 

 ing basis, it will be seen that the former lacks the upper 285 

 feet of the formation. This is a gradient of 6*95 feet per mile 

 * See Ulricli and Schuchert. 



