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.

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    in the fauna is seen at L’Orio'ual, only 10 miles from llawkes- hurv. IFere is found a section less than i^OO feet in thickness, witli sandstone at the base and limestone in the upper ])ortion. The fauna changes abruptly, several s])ecies occurring there which are unknown further east. The ty|)ical Chazy fossils found here are : CamavotaHihiaplena^ Paphistoinn sta/niineum^ and Alalocystites 'nrurchisoni. From this locality west to Alliimette Island, a distance of 115 miles, the same succession of strata may be found, and about the same fauna. All through the Ottawa Yalley the Chazy is rej^resented by a formation which is sandstone at the base and limestone above. In its most western exposures, the limestones are absent and only the sandstone remains. The base of tlie Chazy is always a sandstone, but this does not carry the same fauna in all regions, nor does the zone which rests upon it always have the same fauna. In the Lake Champlain region, the sandstone always contains Lingula hrainevdi ; in the Ottawa Yalley, it carries a modified Cama- roUechiaplena fauna. At the type sections. Lingula hrainerdi is at the base of the formation, while the Camarotoicliiaplena fauna appears TOO feet above. Since the fullest development of limestone deposits of this age is in the region of Chazy and Yalcour Island, New York, that must be the locality in which the Chazy sea persisted longest. From the evidence outlined above, it would seem that this sea was a shallow one, invading south and west over a slowly sinking land. Since the Chazy fauna is apparently developed less directly from the Beekmantown of the Lake Champlain area than from that of Newfoundland, and since there are many European types introduced into the Chazy, it seems probable that this sea was open to the east. If the sea were thus invading upon the land, the sandstone would represent shore conditions. This is undoubtedly the case, for the sandstone in both the Champlain and Ottawa valleys frecpiently presents evidences of shore origin in cross bedding, idpple marks, and worm burrows. If the sea were invading southward in the region now occu- pied by the Champlain Yalley, the sandstone should be younger and younger in age as it is traced from north to south. Tliat this is actually the case is shown by tlie faunas, for at Yalcour Island all the strata of the HelerteUa exfoliata division, 300 feet in thickness, were deposited before the ALaclurites magna fauna became prominent, while at Crown Point this second fauna follows imn’iediately upon the basal sandstone. Dui’ing the greater part of Chazy time, the transgression is southward, but later the shoi’e began to move westward also. The region of the Ottawa Yalley was then invaded, and the