24 NEW YORK STATE MUSEUM 



There are but few outcrops of the Moscow shale in the Owasco 

 lake valley within the limits of the Genoa quadrangle but a few miles 

 farther south in the ravines near Moravia the formation is well ex- 

 posed. 



Tully limestone 



From near the west shore of Canandaigua lake in the town of Gor- 

 ham, Ontario co., to Smyrna, Chenango co., a hundred miles east, the 

 Moscow shales are overlain by the Tully limestone, so named by 

 Vanuxem in his report on the geology of the Third District for 1838. 



On these quadrangles the formation is composed of four to six: 

 compact layers of fine grained blue black limestone that weathers to 

 a light gray or ashen color and has an aggregate thickness varying 

 between 14 and 21 feet. The rock is very hard when fresh but after 

 long exposure breaks easily into small angular fragments. The basal 

 layer which is very hard is 7 to 9 feet thick at some exposures, the 

 others varying from i to 4 feet. Frequent joints divide the strata 

 into large blocks that become detached and are strewn along the lake 

 shores at the base of cliffs in which the limestone occurs and in the 

 bottom of many ravines below cascades produced by it. 



The passage from the soft Moscow shale tO' the base of the lime- 

 stone is very abrupt but at the top the overlying Genesee shale is 

 quite calcareous for a few feet. 



At the top of the low fall where Taghanic creek flows over the 

 limestone at Taghanic point the normal Tully is overlain by 2 feet 

 4 inches of dark impure limestone succeeded by about the same thick- 

 ness of densely black Genesee shale that is succeeded by a 12 inch 

 stratum of dark limestone exposed in the sides and bottom of 

 the stream for about half a mile. As the few fossils in these cal- 

 careous layers are of species common in the Genesee shales they 

 are assigned to that formation. 



Exposures. The Tully limestone is exposed for several miles 

 in the cliffs along the shores of Cayuga lake and in a large number of 

 ravines cut in the hills it forms the crests of falls or cascades and ap- 

 pears in the rock walls, the hard light colored limestone projecting 

 from the dark soft shales and producing the most striking and pic- 

 turesque effects. 



It emerges, forming a low cliff, on the west side of the lake ^ mile 

 from the south line of the quadrangle, rises rapidly to 144 feet above 

 lake level in Willow creek, then descends to lake level half a mile 

 north of Taghanic point. It is submerged for 3}^ miles, then appears 

 in a cliff to Little point and in all the ravines to Barnum creek where 



