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NEW YORK STATE MUSEUM 



pact layers has been quarried extensively in Cornwells gully, in the 

 north part of Penn Yan and along the upper part of the Sartwell 

 ravine i mile south of that village. 



These sandstones are broad lentils, usually becoming thinner 

 and pinching out entirely in one direction and in the opposite after 

 extending a considerable distance of perhaps several miles losing 

 thickness by becoming shaly in the upper or lower part. 



They are the most prominent features in the stratigraphy of the 

 formation and by their superior resistance to the eroding power 

 of the streams as contrasted with the soft shales in the ravines 

 have produced the numerous cascades and waterfalls that contri- 

 bute so largely -to the beauty of the scenery in the region about 

 Keuka lake. 



In the Cashaqua shale is the 



Parrish limestone 



i 



This limestone is interstratified in the Cashaqua shales 25 

 feet below the top in the western part of the Penn Yan quad- 

 rangle, but the shale intervening between it and the overlying 

 Rhinestreet shale thins out rapidly toward the south and east 

 and disappears entirely a few miles beyond the east line of the 

 Hammondsport quadrangle. 



This peculiar formation is an impure concretionary limestone 

 which, in the Parrish gully near Naples, is 4 inches thick and is 

 rich in goniatites and other cephalopods. It does not extend 

 west of the Naples valley but increases toward the east and south 

 and reaches its greatest development, so far as exposed, about the 

 head of Keuka lake. It is 6 inches thick in the gully at Friend, 

 10 inches in the Belknap gully at Guyanoga and in Wagener 

 gully near Pulteney 1 foot, 6 inches. In the ravine at Gibson 

 Landing at 290 feet above the lake it is in four layers aggregating 

 2 feet, 6 inches. It dips under the water on the west side of the 

 lake 50 rods south of Oak point and on the east side a mile farther 

 south and directly opposite Hammondsport. In the small ravine 

 on the east side at Rye point it is 100 feet above the lake, in the 

 large ravine opposite Glen Grove 165 feet and in another, opposite 

 Urbana, it is 6 inches thick and forms the crest of a 25 foot fall 

 211 feet above the lake level. It doubtless extends some distance 

 farther north and east but changes in character to a calcareous 

 nodular shale that does not resist erosion and rarely appears in 

 outcrops. In Hewitts glen, 5 miles south of Penn Yan, it occurs 

 as a shaly and lumpy limestone at 1000 A. T. 



