298 E. BRAINERD THE CHAZY FORMATION. 



3. Massive beds crowded with Orthis costalis, Hall . . 75 feet. 



4. Crinoidal beds with the layer of univalves and the layer of red- 



spotted marble; Columnaria parva. Bill., occurs near the 



top . . . . . . . .70 feet. 



Total exposure ..... 223 feet. 



The Maclurea beds that follow are like those in the two former sections, 

 but of less thickness. The gray oolitic bed is here at the base of the group 

 and is largely quarried for ornamental marble. The overlying strata afford 

 an excellent black marble much used for tiling. 



The upper portion of Group B is assimilated at Isle La Motte to the 

 lower portion of Group C. It consists of dove-colored, fine-grained lime- 

 stone, almost devoid of bedding, rarely containing Maclurea mag)ia, but full 

 of large, light-colored wavy masses resembling Stromatocerinm. Above this 

 appears the ordinary "dove" limestone, with bands of magnesian limestone. 

 We find here : Cyrtoceras hoycli, AVhitfield ; Orthoceras titan, Hall (?) ; Pla- 

 coparia multicostata, Hall; Lichas champlainensis, Whitfield; Ilkeniis, sp. 

 und. ; Bucanla, sp. und. 



The upper portion of the Chazy at Isle La Motte is abraded and covered 

 by a marsh, north of which the Black River and Trenton appear. The dip 

 and strike are the same on both sides of the marsh. If we take this to be 

 the dip and strike of the concealed strata, the total thickness of the Chazy 

 at Isle La Motte would be 640 feet. 



Highgate and St. Armand Section. — As we proceed northeastwardly from 

 Isle La Motte, we pass over Utica and Hudson River slate for fifteen 

 miles, until we reach the eastern shore of Missisquoi bay. The rocks of this 

 tract have been mapped and described by Sir William Logan, and we shall 

 adopt his estimates of thickness in our attempt to correlate these strata with 

 those already described. 



The lowest rock at Highgate springs is a dove-gray, compact pure lime- 

 stone, interstratified in the upper portions with bauds of buflf-weathering 

 dolomite from one to three feet thick. No fossils occur, but in lithological 

 features the strata closely resemble the lower part of Group C at Isle La 

 Motte. This is followed first by fifty feet of greenish-gray, calcareous, fine- 

 grained sandstone, and then by sixty feet of blackish, thin-bedded, shaly, 

 nodular limestones, partially magnesian, containing Ptilodictya fenestrata, 

 Orthis platys, and Aiapyx lialli. Resting upon this come the Black River 

 and the Trenton. The sandstone and shaly nodular limestones have, there- 

 fore, the stratigraphical position of the Rhyiichonella-heanng beds seen on the 

 opposite side of the lake. 



The representatives of the Middle Chazy and Lower Chazy, we believe, are 

 found in St. Armand and Staubridge, just across the boundary line. We 

 have elsewhere indicated that the lower portion (about 1,100 feet) of the 



