540 NEW YORK STATE MUSEUM 



dolomite and shale and the shells of Obolella prima and 

 Hyolithes primordialis (?). 



Above the Hyolithes bed is a band of irregularly bedded 

 sandstone limited above and below by bands of greenish argil- 

 laceous sandstone, and containing pebbles of brown shale and 

 dolomite. This is the zone of Ptychoparia minuta and 

 Conocephalites verrucosus, and holds, besides 

 these species, Lingulepis minima, Lingulella acu- 

 minata, Obolella prima. 



Above this zone Lingulella and Obolella occur at frequent 

 intervals throughout 90 feet of the section to within 50 feet 

 of the top. No other trilobite-bearing bed, and no gastropods 

 were found at higher horizons in this section and we are led 

 to think that the highest horizon of this Ausable section is 

 below that of the Ophileta bed of the Potsdam at Kent Falls. 



The total estimate of the thickness of the formation at this 

 section must fall considerably below its actual thickness which 

 probably will never be determined because of frequent and pro- 

 found faulting. The measured thickness is at least 455 feet, of 

 which a lower portion, 210 feet, is in the south block, and a 

 higher portion of 245 feet in the middle block. Of this thick- 

 ness the upper 110 feet contains the typical Potsdam fauna, 

 without any indications of Siluric relationships. To this total 

 may be added 15 feet, the thickness of the basal beds west of 

 Keeseville, which brings the measured section, with exclusion 

 of all doubtful beds, up to 470 feet. 



Willsboro section 



The Potsdam sandstone has been reported by J. F. Kemp and 

 the late T. G. White (1894), as occurring in close proximity to 

 the Beekmantown in the valley of the Bouquet river at the vil- 

 lage of Willsboro, and on the shore of Lake Champlain near 

 the mouth of the river. The exposures mentioned by the above 

 authors were examined with the result that all the rock cropping 

 out in the river near the village proves to belong within the 

 limits of the Beekmantown series. Down the river, below the 



