24 NEW YORK STATE MUSEUM 



not affected by exposure but in cliff faces is usually disintegrated. 

 This singular deposit is exposed in the ravines on the east side of 

 the lake from Gooding landing southward to Fishers and in the 

 shore cliffs to the Gorham-Middlesex boundary. On the west side 

 from just south of Black point along the shore and northward in 

 ravines at Grange landing, Victoria glen, Foster point and Men- 

 teth point ; also following the Moscow shales in the localities in 

 the Bristol valley already cited. This layer of iron pyrites is con- 

 tinuous from this region westward to Lake Erie and indicates 

 with striking persistence the horizon of the Tully limestone as a 

 plane of division between the Hamilton group of formations be- 

 neath and the Genesee above. 



The Tully limestone itself as exposed in Ontario county locali- 

 ties to the east is a very dark bluish gray rock weathering at first 

 to lighter shades of blue and after long exposure to an ashen gray. 

 It is in two or three layers that are very hard and apparently 

 compact when freshly quarried. On exposure the rock checks 

 along irregular seams and develops a tendency to split into irregu- 

 lar angular fragments an inch or two in diameter. It has been 

 used for construction stone and at one time was burned for quick- 

 lime near the village of Gorham. On Fish creek li miles directly 

 east of Reed Corners, where the highway crosses a small brook, is 

 an exposure showing 4 feet and 2 inches of the limestone, and this 

 exposure seems to have been noted in the report by Professor Hall 

 on the geology of this region in 1843, then regarded as the most 

 westerly appearance of the rock. A more extensive exposure is 

 shown however on lot 53, 1 mile southwest of Reed Corners where 

 the north and south " middle road " crosses a small brook flowing 

 west into Canandaigua lake from a ravine about 40 feet deep and 

 50 rods long above the highway. Here the limestone forms a floor 

 in the ravine for 2 rods and produces a cascade 8 feet high. The 

 exposure continues for 10 to 12 rods on both sides of the gully 

 and at the cascade the total thickness is 5 feet, 10 inches. Still 

 another outcrop is found 2 miles south of the latter on the lake 

 road from Rushville to Canandaigua near the residence of Mr 

 Merritt Cole. This is the outcrop referred to as being near the 



