12 NEW YORK STATE MUSEUM 



marked throughout western New York by a band of gray sandstone 

 which at Rochester is 5 feet thick. This upper stratum has long 

 been referred to as the " gray band " of the Medina. 



In the Rochester region the changes so well marked to the east 

 and the west are not well shown and the red color of the rock is 

 retained up to the "gray band." In the Genesee gorge the upper 

 division of the Medina comprises a series of .sandstones with some 

 interbedded shaly material. The harder projecting beds of sand- 

 stones are shown in the cliffs at the lower falls. 



The thickness which may with certainty be ascribed to the upper 

 division is about 60 feet, but on the basis of the adjoining sections 

 ■the whole distance represented by the hight of the falls, which is 96 

 feet, should be included in the upper division. 



The sandstones at the top of the Medina often show ripple marks 

 and a cross lamination which makes the rock appear to be inclined. 

 These are both indicative of shallow-water conditions at the time of 

 deposition. 



Fossils are not numerous in the upper Medina at Rochester. 

 Fucoides harlani Hall (=A rthrophycus alleghani- 

 ensis Harlan) is the most interesting and occurs in the layers 

 below the " gray band." It is an abundant fossil and has a wide dis- 

 tribution in the upper Medina, to which it appears to be confined and 

 thus serves as an excellent horizon marker. It is known from the 

 Medina of Pennsylvania and Virginia. Though usually regarded as 

 a marine plant it has recently been shown by C. J. Sarle ^ to be of 

 burrow origin and probably Annelidan. 



The closing phase of Medina time is represented by the "gray 

 band," which is excellently shown at the lower falls, where this gray 

 layer shows in marked contrast between the Clinton shales above and 

 the red Medina below. 



The sandstones of the upper Medina are of great economic import- 

 ance. The excellent quality of this stone for structural and street 

 work has given it a wide reputation. All the sandstone quarries 

 between the Genesee and the Niagara rivers are in the upper division 

 of the Medina. 



Clinton formation. This series of rocks follows directly above 

 the Medina. The name is from tlie village of Clinton in central 

 New York where these beds attain a thickness of about 175 feet. 



I Roch. Acad. Sci. Proc. 1906. 4: 203. 



