138 THE CANADIAN NATURALIST. [Vol. 



IV. THE MEDINA FORMATION. 



In referring- to the Geological Reports of tlie St;ite of New 

 York, we learn that the Medina formation rests on what is 

 known as " Oneida Conglomerate," which in Oneida County has 

 •only a thickness of 25 feet, though elsewhere it is as much as 

 100 feet thick, while in the State of Pennsylvania it is developed 

 to the extent of 700 feet. There appears to have been a gradual 

 passage from the band of gray sandstone, terminating the Hud- 

 son River formation in Oneida and Oswego counties, to the 

 overlying conglomerate, both of which deposits, however, are 

 wanting in the western part of the State, and are entirely absent 

 from the series in Canada, as indicated at a short distance east 

 of Oakville, on the north-western side of Lake Ontario, where 

 the upper beds belonging to the close of the Cambro-Silurian Age 

 are seen to rest beneath those at the commencement of Medina 

 epoch. 



In tracing the Medina formation from Oswego County, N.Y., 

 it is found to increase in thickness until it attains a development 

 of several hundred feet in the western part of the State, and at 

 Dundas. at the head of Lake Ontario, it is 545 feet thick. 

 Again the group gradually dies out to the westward, and is only 

 represented in the State of Ohio by ten or twenty feet of red and 

 blue mottled shales. 



Almost the whole series is made up of more or less calcareous 

 shales, some of which are also arenaceous (and almost resemble 

 thin flags of unpure sandstone). In color the shales are red, 

 green, or variegated. The series is cappf^d by a coarse sandstone, 

 which is irregularly deposited and has a thickness in the region 

 of Dundas and Hamilton, varying from seven to ten feet. It is 

 known by the name of the "Gray Band," and is a characteristic 

 stratum from the Niagara River to the Georgian Bay. Some- 

 times, however, it thins out to mere wedges, bnt the hollows 

 occasioned by the sudden thinning process is filled up with earthy 

 calcareous sandstones. This structure is well illustrated by a 

 section in the glen just west of the Sydenham road, Dundas — 

 the following section would not be represented longitudinally by 

 more than thirty feet: 



