P. E. Raymond — Fauna of the Chazy Limestone. 355 



feet at Yalcour Island. Further north the thickness is not 

 definitely known. In the Ottawa Valley, the formation is 

 usually from 100 to 200 feet thick and is about half limestone 

 and half sandstone, the former usually overlying the latter. 

 At the Mingan Islands, the thickness was estimated by Sir 

 William Logan at about 300 feet, and the strata include both 

 shales and limestone. 



Lake Champlain Region. 



As the typical Chazy is exposed in the Lake Champlain 

 region, that area will be first taken up. In general, the Chazy 

 rocks are seen as a narrow belt running almost north and 

 south from Orwell, Vermont, to Joliette, Canada. The area 

 is seldom more than 10 miles wide, and is not a continuous 

 exposure, but occurs in small patches, in most cases evidently 

 fault blocks, and the strata are usually inclined at a consider- 

 able angle. The principal outcrops are along the west side of 

 Lake Champlain and on the islands in the northern part of 

 the lake. South of Willsboro Point, there are scattered 

 patches on both sides of the lake nearly to Fort Ticonderoga. 



Faunal Divisio?is. 



In the Lake Champlain region, three major faunal divisions 

 of the Chazy may be distinguished. Within these, there are 

 again various zones which are more or less local in geographi- 

 cal extent. 



Division 1. The Hebertella exfoliata Division. — The strata 

 of this basal division are chiefly light-colored, impure, rather 

 coarse-grained limestones and frequently have shaly partings. 

 The thickness varies from nothing at the south end of Lake 

 Champlain to 300 feet on Valcour Island, 365 -f at Chazy, and 

 225 feet on Isle La Motte. 



The characteristic fossils are : Hebertella exfoliata sp. no v., 

 Orthis acutiplieata sp. no v., Strophomena prisca sp. no v., 

 Scenella pretensa sp. nov., 8. montrealensis, Palceacmcea irregu- 

 laris sp. nov., Paphistoma immatura, and Sealites angulatus. 

 Other species occurring abundantly in this zone are : Blastoi- 

 docrinus carcharicedens, Dolboporites americanus, Zygospira 

 acutirostris, Paphistoma stamineum^ Lophospira subabbre- 

 viata, Bucania sulcatina, and Pseudosphcerexochns chazy ensis. 

 Those which occur only rarely in this division, but which thus 

 far have not been found in higher divisions, are : Lingula 

 belli, Cyrtodonta solitaria sp. nov., Cyclonem a ? nor maliana 

 sp. nov., Eanema leptonotum sp. nov., and Heliomera sol. 



Of the 141 species m the Chazy whose range is known, 64 

 make their first appearance in this horizon and 23 are found in 



