BEEKMANTOWN AND CHAZY FORMATIONS OF CHAM PLAIN BASIN 397 



2 Sections for reference 



Since the majority of the cephalopods here described have been 

 obtained from the shore at Yalcour, south of Plattsburg, we insert 

 here for reference a brief section of the exposures in which the cepha- 

 lopods both of the upper Beekmantown and lower Chazy are found 

 to occur more profusely and better preserved than in any other 

 locality on the west shore of the lake, known to the writer. A fuller 

 discussion of the important Yalcour section is necessarily deferred 

 until the investigation of the Beekmantown and Chazy faunas has 

 been completed. The major part of this material has been jointly 

 collected by Prof. G. van Ingen and the writer during the summer 

 of 1899; a number of valuable specimens have also been obtained 

 by Professor van Ingen during the field season of 1901, and the 

 specimens cited from Beekmantown, Chazy and Yalcour were mostly 

 collected by the writer during the summer of 1903. 



The exposure of the Beekmantown beds on the Yalcour shore 

 begins about one half mile north of the mouth of the Little Ausable 

 river, in front of the farmhouse of W. H. Ayers (Lake Yiew farm) 

 and continues with some interruptions to the Yalcour dock (Port 

 Jackson) where a fault separates it from the exposures of Lower 

 Chazy rocks, which thence continue northward around Day's point. 



The Beekmantown beds have been provisionally distinguished as 

 2065 A^-Ag 1 and the Chazy beds as 2066 B^Bg. 



Section of the Beekmantown beds at Vale our in ascending order 



A 1 is a four foot bed of hard bluish gray, gritty dolomite. Strike, 

 n. 30 e. ; dip, 5 s. e. 



A 2 begins 100 feet north of end of A 1 . 3 feet. Bluish gray 

 dolomite, with lenses of lighter dolomite ; the latter very fossiliferous. 



A.., exposed about 300 feet north of A 2 . 6 feet. This division 

 is shaly at the base, compact, gray or black at the middle and shaly 

 and black at the top. the whole weathering yellowish. The gray 

 portion is a mass of fossil fragments derived from crinoids, trilobites. 

 cephalopods, gastropods and brachiopods, and contains small rounded 

 pebbles or concretions. The shaly portion at the top is a valuable 

 depository of cephalopods (nautilicones and orthoceracones). 



1 This A is not identical with the division A of the Beekmantown of 

 Brainerd and Seely, nor is B, Chazy, identical with their Chazy B. On 

 the contrary the Beekmantown beds at Valconr are undoubtedly equiva- 

 lent to a part of the Fort Cassin beds and therefore probably to be placed 

 at the top of their Group D [see section on p. 399] and the Chazy beds 

 correspond to Brainerd and Seely's upper A of the Chazy. 



