PORTAGE AND NUNDA QUADRANGLES 49 



As usually described in the annual and final reports it immediately 

 overlies the Tully limestone or, when that is wanting, the Moscow 

 shale, and is succeeded by the beds of greenish shale afterward 

 given the name Cashaqua shale, but on page 422 of the report for 

 1839, after mentioning the localities of several exposures of the 

 Upper black shale in the vicinity of Moscow and Geneseo, including 

 the one at Fall brook, where it is stated '' the water leaps a hundred 

 feet from the top of this rock," Hall says: ''In this neighborhood 

 the black shale is succeeded by a stratum "of thin limestone." 



In the final report on the fourth geological district, page 227, 

 where describing the Cashaqua shale he says: "On tracing it (the 

 Cashaqua shale) west of the Genesee, it constantly presents the 

 same features as on the Cashaqua creek, though the lower part is 

 sometimes dark colored and separated from the Genesee slate by a 

 thin calcareous band," evidently referring to the limestones at the 

 top of the falls at Fall brook and in the ravine of Little Beards 

 creek at Moscow which also appear in all exposures of this horizon 

 between Ontario county and Lake Erie, and are now known as the 

 Genundewa limestones, more fully described in the succeeding 

 pages. That it is the stratum referred to by Hall is made certain 

 by the fact that there is no other continuous limestone above it in 

 the Genesee river section, nor elsewhere in this State west of On- 

 tario county. 



There are 83 feet of Genesee black shale between the horizon of 

 the Tully limestone and the Genundewa limestone at Fall brook and 

 100 feet of dark and black shales between the Genundewa lime- 

 stone and the base of the Cashaqua shale at the mouth of the gorge. 

 The latter beds have been commonly known as Upper Genesee, but 

 the difference in the character of the shale above and below the 

 Genundewa limestone, and in their faunas, has made it proper, as 

 further explained in New York State Museum bulletin 63, page 25, 

 to restrict the use of the name '' Genesee " to the beds between the 

 horizon of the Tully limestone and the Genundewa limestone. 



As thus defined the only exposure of this formation on these 

 quadrangles is at the west end of the highway bridge over the 

 Genesee river at Mount Morris in the lower part of a small out- 

 crop on the north side of the bridge. At times of low water the 

 exposure is 15 to 20 feet long and 6 to 8 feet high. 



The shale here is very dark, but somewhat more calcareous and 

 less bituminous than the beds below, which are, for the most part, 

 densely black and on exposure become very fissile and split into 



