10 NEW YORK STATE MUSEUM 



in the rear of A. B. Cooper's residence there are beds of dolomite 

 which, aggregating 8 feet in thickness at the base, are succeeded 

 by 15 feet of dark bluish shale and these are overlain by 6 feet 

 of dolomite like that below. Overlying these layers and exposed 

 for many rods in the bed of the creek is a mass of tough 

 argillaceous limestone 15 feet thick that bears Stromatopora quite 

 abundantly and seems to indicate a western continuation of the 

 well known Stromatopora bed at this horizon in Onondaga 

 county. It is dark brownish gray when freshly broken and 

 usually takes on a darker tinge of brown for a time owing to 

 the exudation of a minute quantity of petroleum but finally 

 turns to a light yellowish drab. It contains many small aggre- 

 gations of selenite crystals, and the boulders from it by reason 

 of their peculiarly tough character have survived glacial transpor- 

 tation and grinding and are strung in great numbers over the 

 contiguous territory to the south, have many small cavities and a 

 general scraggy appearance due to the weathering out of these 

 crystals. 



A bed of shaly dolomite 4 feet thick is the highest member of the 

 group. This appears in the west bank of the creek a short distance 

 below a low fold 60 rods north of the New York Central Railroad 

 bridge at Mertensia. There are several small exposures of these 

 upper beds in this vicinity, the most extensive of which is in the 

 section afforded in the Hog hollow or Great brook ravine on the 

 west side of Bough ton hill, where 25 feet of the top la3'ers are well 

 displayed. The two upper members appear J mile east of Fredon 

 and have been quarried on the land of A. B. Cooper and Hiram 

 Powell, and at the latter place there are the ruins of two limekilns 

 where material from the Stromatopora layer was formerly burned 

 and then hauled to Conover's mill and ground for cement; 

 there are several other abandoned kilns in the vicinity in which 

 quicklime was once produced from the purer layers below. No 

 other exposures of these beds have been observed in this western 

 portion of Ontario county, but they are of more frequent occur- 

 rence eastward, just beyond the line of the quadrangle and are 

 there more freely worked and contain organic remains in greater 



