304 C. SCHUCHERT — MEDINA AND CATARACT FORMATIONS 



stone, and reposing upon it, is a gray sandstone, the lower part often 

 variegated with the red oxide of iron, and the npper variegated with 

 green shale. . . . This mass for position corresponds with the 'mill 

 stone grit' to the east and the 'gray band' to the west." "The 'millstone 

 grit,' which is thirty and more feet in thickness in Herkimer and Oneida, 

 gradually attenuates in going westward, being from four to five feet at 

 Rochester. The materials of which this rock is formed, gravel and sand, 

 prove that their source was eastwardly," It is in the following report 

 (1840, page 374) that he proposes "Oneida conglomerate. The 'mill- 

 stone grit' of Prof. Eaton, which has been changed, to do away with all 

 ambiguity." Here it is, too, that Vanuxem lays aside his term Oswego 

 for "Medina sandstone. Called in former reports the red sandstone of 

 Oswego." 



THE 8ILURIC SECTIONS IN DETAIL FROM ROCHESTER, NEW YORK, TO THE 

 HEAD OF LAKE HURON 



Rochester, New York, section. — Examined by the writer in August, 

 1913. Use has also been made of Hartnagel, Bulletin of the New York 

 State Museum, page 114, 1907, and Hall, Geology of New York, Fourth 

 District, 1843, pages 58-117. 



Lockport dolomite. Thickness present, 107-125 feet. The lowest beds are 

 studied to best advantage in the large quarry on North Goodman 

 street, where the Rochester is also worked for building stone (foun- 

 dations). Here the lower 5 feet of the regulation Lockport consists 

 at the top of fine-grained, dense, crystalliQe dolomite. Downward in 

 this 5 feet appears more and more of sand, and finally the lowest 

 foot or more is a regularly bedded, laminated, filne-grained, brittle 

 sandstone. Beneath is a dark, bituminous, thin-bedded sandy shale, 

 filling the hummocky depressions in the beds below. The same ir- 

 regular contact may be seen at the Upper Falls of the Genesee. 

 De Cew mem'ber (Williams MS., 1914). The top of the Rochester is hum- 

 mocky to the extent of at least 4 feet. Between these depressions 

 and over the top of the ridges is deposited from 2 to 5 feet or slightly 

 more of irregularly bedded (sea-churned) impure limy cement beds, 

 not unlike the Rochester below. 



Irregular wavy contact f Time break, if any, short. 



Rochester shale. Thickness about 85 feet. At Rochester the formation has 

 more lime and the strata are much harder and more resistant to 

 weathering than at Niagara Falls, where there is less lime and the 

 beds are more laminated into thin-bedded shales. 



Clinton formation. Thickness about 80 feet. 



Irondequoit limestone memher, 18 feet thick. Thin-bedded limestones 

 with shale partings. Locally between Rochester and Niagara Falls 

 small Bryozoa reefs are developed near the top of this member, and 

 some of these project several feet into the Rochester shale. Other- 



