98 ROCHESTER ACADEMY OF SCIENCE. [J-^^'- 'I. 



d. Hall's "vertical section" of 1838 gave 180' of "bituminous shales 

 containing septaria " in the vicinity of Mt. Morris (2d An. Rept. 

 Fourth Geol. Dist. N. Y.) ; but this probably included the recur- 

 ring black shales in the lower Portage. In 1839 the thickness of 

 the upper Black shale (Genesee), in Seneca Co., was given as 150' 

 (3d An. Rept. Fourth Geol. Dist. N. Y., p. 301). While in the 

 final report Professor Hall said : " On the shores of Seneca lake 

 and in Ontario county the thickness of this rock is about 150 

 feet. * * * * After passing the Genesee river in a westerly 

 direction, it soon becomes evident that the rock has diminished 

 in thickness. * * * * q^ thg shore of Lake Erie * * * 

 [it] is but twenty-three feet seven inches " (Geol. N. Y., Pt. IV^ 

 p. 221). Dr. Clarke gives the thickness as 160' along the shores 

 of Canandaigua lake (Bull. U. S. Geol. Surv., No. 16, pp. 13, 14). 

 With the thickness on Canandaigua lake 160' and on Lake Erie 

 nearly 24', if the decrease in thickness were uniform then north 

 of Warsaw the Genesee would be about 92' thick. In the James- 

 town well it is about 65' (Harris, Am. Geol., Vol. VII, pi. 4 ; see 

 p. 169). 



e. The Tully limestone does not reach the Genesee river and conse- 



quently the next lower formation in this section is the Hamilton. 

 Professor Hall wrote in 1839: "The Tully limestone I have 

 observed but at two points in Ontario county ; one in the bed of 

 Flint creek at Bethel [now Gorham], * * * * ^j^g 

 other four miles northwest of that village " (3d An. Rept. Fourth 

 Geol. Dist. N. Y., p. 313). In the final report the Professor said : 

 " On Canandaigua lake, it [Tully] is represented by a few inches 

 of impure calcareous matter," and further : " This rock is virtually 

 absent at all places west of Canandaigua lake " (Geol. N. Y., 

 Pt. IV, p. 213). Dr. Clarke says: "This formation [Tully] is 

 lacking in New York west of the village of Bethel, in the town- 

 ship of Gorham, but for a distance of ten or fifteen miles west of 

 its last appearance its influence seems marked by the clearly 

 defined separation between the shales of the Genesee and those 

 of the underlying Hamilton " (Bull. U. S. Geol. Surv., No. 16, p. 

 17). Finally, in reference to the distribution of the Tully see 

 the map of the "Geographical distribution of the Tully lime- 

 stone, in central New York " by Prof. S. G. Williams in the Sixth 

 An. Rept. State Geologist [N. Y.] for 1886 ; also, p, 14. 



Prof. Hall on the " vertical section " of 1838 gave 400' as 



