GEOLOGY OP THE NORTHERN ADIRONDACK REGION 3G5 



Chazy formation. The Cliazy rocks are found, at the present 

 day, only on the eastern border of the Adirondack region. Their 

 present distribution gives but little idea of tlie extent of the sea 

 in which they were deposited, which must have encroached widely 

 over the present northeastern portion of the Adirondacks, from 

 which the deposits have been since removed b}'^ erosion. But the 

 formation is wholly lacking on the remaining sides of the region, 

 and can not have been laid down there at all. On the contrary, 

 the Beekmantown land area of the southern and western parts 

 of the region became greatly extended in those directions, shutting 

 out the sea altogether, and leaving merely the eastern area sub- 

 merged during this time. 



Much detailed study has been given the Chazy formation 

 throughout the Champlain valley by Brainard and Seeley.^ For 

 stratigraphic detail and accuracy this work can not be improved 

 on. It shows that the formation is thickest in the latitude of 

 southern Clinton county ; that it rapidly thins southward to utter 

 disappearance at the upper end of Lake Champlain; and that it 

 also thins nortliwaird and moreover changes considerably in char- 

 acter in this direction. 



Throughout most of the Champlain valley the formation con- 

 sists essentially of beds of quite pure, clear water limestones, 

 with a surprisingly small amount of land wash of any sort, in 

 itself <an indication of considerable width for the basin, much 

 beyond what the present breadth of outcrop would indicate. The 

 formation is thickest on Valcour island, and Brainard and 

 Seeley's measured section there is here reproduced. 



Group A (Lower Chazy) 



Feet 



1 Gray or drab sandstone, interstratified with thin (or some- 



times thick) layers of slate, and with occasional thin 

 layers of limestone at the base, containing G a m e - 

 rella (?) costata Bill 56 



2 The slaty sandstone gradually passes into massive beds, 



made up of thin alternating layers of tough slate and 

 nodular limestone, containing undetermined species of 

 Orthis and Orthoceras 82 



^Am. Geol. 2 :323-30 ; Geol. Soc. Am. Bui. 2 :293^30O ; Am. Mus. Nat. Hist. 

 Bui. 8:305-1.5. 



