GEOLOGY OF THE GENEVA-OVID QUADRANGLES 



25 



of the ridge that separates the Seneca from the Cayuga lake val- 

 ley, 840 feet A. T., 395 feet higher than in the depression where it 

 last appears on the lake shore 3^ miles west and but 2 miles 

 farther south. 



From this point it descends to 800 feet A. T. in an outcrop near 

 the railroad station at Hayt Corners; 715 feet A. T. in Fall creek; 

 680 feet A. T. in the next ravine south, and 640 feet A. T. under 

 the bridge over the third ravine, or 160 feet in 1% miles east and 

 Y$ mile south. 



At the top of the falls in the Barnum creek ravine it is 680 feet 

 A. T. dipping as everywhere in this immediate vicinity at the rate 

 of 100 to 150 feet per mile toward the' southeast. It disappears 

 under Cayuga lake 381 feet A. T. }i of a mile southeast of Little 

 point and 10 miles southeast of its last outcrop on these quadrangles. 



Fossils are not generally common in the Tully limestone, but 

 usually may be found in one or more of the layers in considerable 

 numbers at each outcrop. 



These are in matter of number species of the fauna below but 

 the presence of the brachiopod Hypothyris cuboides 

 Sowerby (Rhynchonella venustula Hall) gives it 

 definite stamp as a formation which must be regarded the earliest 

 member of the Upper Devonic. 



Genesee shale 



In the annual and final reports of the fourth geological district, 

 Professor Hall considered the heavy bed of black and dark shales 

 that succeeds the Tully limestone as constituting one formation 

 known at first as the " Upper black shale " to distinguish it from 

 the Lower or Marcellus shale, but later designated " Genesee shale " 

 from its exposure in the Genesee valley. He recognized, however, 

 a marked difference between the upper and lower beds in both 

 lithologic character and the fossils they contain, referring to them 

 frequently as " Upper Genesee " and " Lower Genesee." 



On page 422 of the report for 1839 he says : " In this neighbor- 

 hood, (the Genesee valley in the vicinity of Geneseo) the black 

 shale is succeeded by a thin stratum of limestone." Subsequent in- 

 vestigations under his direction have shown this to be the Genun- 

 dewa (Styliola) limestone, which is continuous from Ontario county 

 to Lake Erie, interstratified not far from the middle of the beds 

 and that it is the only continuous layer of limestone in that region 

 above the Tichenor limestone. 



