524 PROCEEDINGS OF THE WASHINGTON MEETING 



color and smelling strongly of petroleum on freshly fractured surfaces. Some of 

 its layers are separated by thin shale films. Fossils occur rather abundantly in 

 certain layers, and in the coarser parts an occasional small quartz pebble is found. 

 The region in which it occurs above waterlevel is glaciated, and almost all cf its 

 outcrops are concealed by till. It extends from North Cuba and Ischua, however, 

 down Oil and Ischua creeks to near their junction where its dip carries it beneath 

 floodplain level. A solitary exposure is found in a railway cut north of Great 

 valley, on the Salamanca quadrangle. 



From its exposure in quarries in and around Cuba this sandstone is known as 

 the Cuba sandstone. It is regarded as a lentil in the Chemung formation. 



Above the Cuba sandstone lentil, the Chemung is composed of green and brownish 

 argillaceous and sandy shales, interbedded here and there with thin shaly sand- 

 stones. With the probable exception of certain dark purplish shales to be de- 

 scribed presently, the individual beds of neither the shales nor the shaly sand- 

 stones usually retain their thickness or individuality or possess any lithological 

 character that w^ould enable any one of them to be traced and identified for any 

 distance. The nearest approach to persistency in these variable beds is found in 

 a sandy zone about 200 feet above the Cuba sandstone. A number of quarries 

 have been opened in the past on some argillaceous sandstone at this horizon; 

 but even this sandy zone, persistent as it is as a whole, well illustrates the varia- 

 bility in detail of these Chemung strata, for often in one quarry face there is 

 visible a complete change along the bedding plane from one lithological phase to 

 another, so that as a whole these Chemung shales and argillaceous sandstones are 

 only regular in their irregularity and intergradation. 



The one exception as regards the rapid variability of these shales is found in cer- 

 tain dark purple or chocolate colored shales about 325 to 350 feet below the top of 

 the Chemung. They seem to be widely persistent and are found in many well 

 borings to the south. Their top occurs in the Dennis well at Bradford, Pennsyl- 

 vania, at a depth of 712 feet. 



At a number of horizons the shales become locally calcareous and a few inches 

 of them may pass into a very impure limestone that where exposed on the surface 

 has usually been leached out into a honey-combed mass of brachiopod casts and 

 molds. Ripple markings are common at various horizons, and in a few places 

 what may possibly be obscure mud cracks are found. 



CATTARAUGUS 



Wolf Creek conglomerate lentil. — A marked change in the conditions of sedimenta- 

 tion caused the deposition of a conglomerate that is most prominently developed 

 on Wolf creek and is known as the Wolf Creek conglomerate. Its pebbles are 

 predominantly flat or discoid, and hence it is also often called the " flat-pebble" 

 conglomerate in contradistinction to the Glean or " round-pebble" conglomerate 

 occurring higher in the series. The pebbles are mostly of vein quartz, though a 

 few are of red jasper. The mass of the rock is, as a rule, a coarse, loosely ce- 

 mented, cross-bedded sand sometimes bleached white, but usually stained yellow 

 or brown by iron. One of the most prominent characteristics of this conglomerate 

 is its rapid variation in thickness. Nowhere more than about 20 feet thick, it often 

 in a few hundred yards thins down to a few inches in thickness. Notwithstanding 

 ts rapid variation in thickness it was found to be a remarkably persistent stratum 



