Raymond: The Chazy Formation and its Fauna. o()3 



Beekmantown fauna of the region of Lake Champlain, is, however, 

 exceedingly incomplete, so it is not possible to make comparisons at 

 the present time which will hold good when the Ueekniantown fauna is 

 thoroughly studied. 



It can be said, however, that there is an almost comjjlete change 

 of species between the two formations, as only one species which is 

 common to the two formations has so far been found. The most 

 marked difference between the two faunas lies, however, in the general 

 composition. In the Beekmantown, bryozoans, crinoids, cystids, and 

 lamellibranchs are almost unknown. The brachiopods are few in 

 numbers, and are represented by small forms including such (."ambrian 

 types as Billingsella and Syiitroplda. In the Chazy, new types of 

 brachiopods are introduced for the first time, such as Rafinesquina, Stro- 

 plioiiiciia and Camarota'chia, genera which became very imijortant in 

 later faunas. Among the gastropods, Bucania and Cyrtospira are genera 

 which make their first appearance in the Chazy and become more 

 abundant later. The trilobites of the Beekmantown and Chazy have 

 been compared in a previous article where it was shown that in that 

 group there was little similarity between the two formations. 



While the Black River and Trenton formations have only a few spe- 

 cies in common with the Chazy, yet when the fossils are compared 

 with one another it is found that almost every one in the Chazy is 

 represented in the Trenton by a very closely allied species. W^ith the 

 exception of Blastoidocriints, Malocystites, Glaphiints, Helioinera, 

 Batliyiirellus zxvA Pliomei-ops , the genera pass into the formation above. 



Faiinal Divisions. 

 In the Lake Champlain region there may be distinguished three 

 great faunal divisions of the Chazy. In these divisions, there are again 

 various zones which are, however, more or less local geographically. 



Division i : Tlic Hcl'crtella cxfoliata Division. 



The strata of this basal division are chiefly light-colored, impure, 

 rather coarse-grained limestone. They are often heavy-bedded and 

 frequently have shaly partings. I'he thickness varies from nothing at 

 the south end of Lake Champlain to 300 feet at Valcour Island, 

 365 + at Chazy and 225 feet on Isle La Motte. 



Characteristic fossils are : Hebertella exfoliata, Orfliis acutipliiata, 



