1002 NEW YORK STATE MUSEUM 



common, and a few fish scales and plates have been found, but 

 otherwise they are generally barren. A few small Lingulas 

 (L. spatulata, L. ligea) found at the mouth of Pike creek 

 on Lake Erie are the only fossils collected from this horizon, 

 and they seem to belong to the species found in similar black 

 shales higher in the formation. 



This bed .of black shales has quite the same structure and 

 appearance as other black bands in the Portage section. 



Above this horizon there is no recurrence of the Genesee 

 fauna. 



The bottom of the passage beds immediately below the black 

 band is therefore taken as the base of the Portage formation, 

 and the stratum of black shales above has been designated 

 by the state paleontologist as the Middlesex shales. 



Middlesex black shales. This bed decreases slightly in thick- 

 ness toward the west, but is thicker and quite arenaceous in the 

 Dansville and Naples valleys. It is exposed in the cliffs on both 

 sides of the Genesee river, from the mouth southward for a 

 little more than two miles, the dip bringing it down to the water 

 level on the south side of the " Hogsback." 



Near the top, after several alternations with lighter layers in 

 a few feet, these shales are replaced by light bluish gray, and 

 olive shales, " soft argillaceous rock of a green color " (Hall). 



Cashaqua shales. This mass is 165 feet thick, and was termed 

 by Hall the Cashaqua shales because of their excellent exposure 

 in detail in the gorge of Cashaqua creek, 5 miles east of the 

 Genesee river. 



The general color of this shale in weathered exposures is a 

 very light olive; but, when freshly excavated, it is medium dark 

 bluish gray with frequent intercalations of darker or black 

 layers of varying thickness, sometimes so thin and frequent as 

 to give the rock a straticulate or laminated structure. 



In the section along Cashaqua creek there are a few thin 

 flags in this horizon, and they increase in number toward the 

 east. They are hardly noticeable in the Genesee river section. 



Uneven concretionary and more or less calcareous layers from 

 1 inch to 4 inches thick occur frequently, and some of them 

 are continuous for many rods. Spheric and elongated concre- 



