KELATION OF TULLY LIMESTONE AND GENESEE SHALE 951 



lioliiia shells. The basal part of the Genesee is well shown on the western 

 bank, where the Tully band, rising northward from the water, makes a 

 prominent cliif. The black shale can be seen to grade downward into 

 gray, calcareons shales in which Chonetes and Orthoceras occur. The 

 rock is still a shale, bnt some layers are resistant enough to form shelves 

 at the water level. These layers are generally about six inches thick and 

 are separated by fissile shale layers, which layers are in general of a 

 blacker color than the harder, more calcareous beds, though their color is 

 not as deep as that of the typical Genesee. Downward the calcareous 

 layers become more solid and the shales separating them are less black in 

 color. The entire thickness of this transition series is about eight feet 

 and below it the Tully limestone proper occurs. This rests on the fossil- 

 iferous Moscow shales, which in turn are underlain by the Tichenor lime- 

 stone. It is here very evident that the contact of the Tully and the Gen- 

 esee is a gradational one, the Genesee type of sedimentation gradually 

 replacing the Tully type; also, since only the lower part of the Tully is 

 calcareous in the Ithaca region, the upper part must be represented by 

 the Genesee type of sedimentation. From this it appears that the Genesee 

 type of sediment was gradually and progressively replacing the Tully 

 type to the northward. 



Southward Disappearance of the Tully Limestone 



The Tully limestone disappears entirely a short distance south of the 

 Pennsylvania line, beyond which only black shale of the Genesee type is 

 found. 



In the Catawissa section of Columbia County, Pennsylvania, the Ham- 

 ilton group is terminated by a somewhat calcareous series 25 feet in thick- 

 ness, with a normal Hamilton fauna. This is succeeded by 225 feet of 

 bluish black fissile shales, which have the character of the Genesee and 

 are to all appearance barren of fossils. This, in turn, is succeeded by 25 

 feet of dark blue, shaly sandy beds without fossils, which represent the 

 closing stages of Sherburne sedimentation. Next above this are 175 feet 

 of shales and sands carrying the l^aples fauna and with many included 

 plant remains, and then follow 1,400 feet of shales in which the Ithaca 

 fauna holds sway. 



This section is due south of Ithaca, and it apparently marks the line of 

 maximum deposition of the Genesee type of sediment. It is significant 

 of the conditions of the sedimentation that marine fossils are on the whole 

 very rare in these shales, while plant fragments and spores are not un- 

 common. 



