298 Review of the New York Geological Reports. 



Its greatest thickness is near Niagara River, where Hall esti- 

 mates it at three hundred and fifty feet. In Canada it is prob- 

 ably still thicker. It gradually becomes thinner in an easterly 

 » direction, and thins out entirely in Oneida County. The scenery 

 in the region of the Medina sandstone is often highly picturesque. 

 The falls of Medina and Genesee are formed by its escarpments. 

 The former of these localities on Oak Orchard Creek, is consid- 

 ered the most interesting for collecting its organic remains ; here 

 also it exhibits Hall's fourfold subdivisions, viz. 



1. Red marl and shaly sandstone. 



2. Grey quartzose sandstone. 



3. Red shale and sandstone. 



4. Greenish grey argillaceous or siliceous sandstone. 



The second subdivision furnishes good flagstones, and is also 

 the fossiliferous portion. Its fossil genera are : Lingula, Cythe- 

 rina, Pleurotomaria, with a few Bellerophon, Cypricardia and 

 Orthoceras ; almost all however abraded and broken, indicating 

 a troubled condition of the sea in which the deposite occurred. 



Hall conjectures that the red deposites above and below this 

 grey, fossiliferous band, were the products of a mud volcano highly 

 charged with oxide of iron and rapidly spreading over the sur- 

 face, rendering the sea turbid and overwhelming all organic forms. 



Diagonal lines of lamination are often strongly marked in the 

 sandy strata at Rochester. Black or dark colored sandy accre- 

 tions, around which the strata have been deposited, are seen in 

 the second subdivision at Lewiston, and oblong or rounded accre- 

 tions of shale are observable also in the third subdivision. 



At the extreme eastern extension of the Medina sandstone, it 

 assumes the form of a conglomerate. 



The soil derived from the formation under consideration is vari- 

 ous ; sometimes sandy, but more frequently a stiff loamy clay sus- 

 ceptible of improvement, and affording by cultivation a fertile soil. 



Small quantities of copper and iron pyrites with oxide of man- 

 ganese and iron, together with carbonate of copper, are the only 

 metallic substances that have been discovered in this rock. At 

 Rochester small spherical masses of reddish sulphate of barytes 

 occur, filling cavities in the rock. 



At Gasport on the Erie Canal, carburetted hydrogen issues 

 from the Medina sandstone in sufficient quantity to light up a 

 large room, but nowhere can it be collected in such abundance 

 as to be of much practical benefit. 



