The fauna of the Chazy limestone / by Percy E. Raymond.

  • Raymond, Percy Edward, 1879-1952.
Date:
[1905]
Catalogue details

Licence: In copyright

Credit: The fauna of the Chazy limestone / by Percy E. Raymond. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    15/32 (page 365)
    First. All tbrouo’li 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 n])per beds were never deposited sooth of Valconi-, the Chazy sea after advancing slowly to the south to some point below ()rwell, Vermont, must have then retreated to the northward. Snch a recedence could have been caused onlv bv an elevation south of Orwell, for there is no general retreat of the Chaz}^ 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 Camarotcechia plena., beds vanished from the area of Lake Champlain. During the latter part of Chazy time or after its close, the Stones Kiver (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 Ileheidella 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 161 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 notliing at Crown Point. This is a thinning out of 7‘3 feet per mile, which, on the other hand, is probal)ly 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 421 feet above it. If this minimum estimate of the height of the base of the Crown 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 Ulrich and Sehuchert.