528 PROCEEDINGS OF THE WASHIXGTOX MEETING 



beneath. Tlie same thing is true at Millers cliff, in AVarren county, Pennsylva- 

 nia, where the Glean occurs, but beneath it the Sub-Olean is wanting. From 

 differences of level in the base of the Olean as exposed in outcrops often but short 

 distances apart, the floor upon which the Olean was deposited must have been a 

 very irregular one. This unconformity separating the Pennsylvanian and the 

 Mississippian series is believed from the work of Mr David White and others to 

 be of widespread occurrence southward in Pennsylvania. 



PO TTS VILLE— OLEAN CONGL OMERA TE 



Next comes a massive round-pebbled conglomerate, widely known as the Olean 

 conglomerate. In texture the Olean often varies quite rapidly, both horizontally 

 and vertically. In some places or in some beds it is scarcely more than a coarse 

 sandstone with a sparing development of pebbles, while at other places or in other 

 layers at the same place it is almost entirely composed of rounded quartz pebbles. 

 It is often strongly cross-bedded. The pebbles are well rounded and, in contrast 

 to the flattened or discoidal pebbles of all of the underlying conglomerates in the 

 region, are predominantly ovoid in shape. Most of the pebbles are of vein quartz ; 

 a few are of a hard, dark gray slate ; none are of red jasper. 



They are embedded in an arkosic matrix, in portions of which there is consider- 

 able iron, which has formed thin, limonitic streaks or crusts through the rock and 

 resists disintegration better than the arkosic cement does. Pebbles of vein quartz 

 on firmly cemented surfaces are sometimes found much etched or corroded. 



Disintegration of the Olean is, as a rule, rapid, and talus slopes conceal the base. 

 Numerous well borings, however, on the Olean quadrangle give an accurate measure 

 of its thickness there, which is usually between 60 and 70 feet, though in one well 

 it is 90 feet. It occurs on the highest hilltops in the southern part of the two 

 quadrangles in a number of small detached areas, and is well known southward 

 in McKean county and westw^ard in Warien county in Pennsylvania. 



Above the Olean conglomerate at Rock City are found a few feet of thin, sandy, 

 furruginous shales, in which some years ago a thin coal bloom was exposed in 

 grading a road. It also belongs to the Potts ville. 



AGE OF THE FORMATIONS 



The extensive collection of fossils made by Mr Charles Butts w^ere studied by 

 him at Albany under Dr J. M. Clarke's supervision. Professor H. S. Williams has 

 also studied similar collections made by himself and his assistants in this region, 

 and the paleontological facts stated below concerning faunal affinities are those 

 ascertained as a result of the investigations of Doctor Clarke, Doctor Williams, and 

 Mr Butts. 



The conclusions which the writer has drawn from these paleontological facts he 

 alone is to be held responsible for. 



The shales extending from the lowest exposures up to the base of the Wolf Creek 

 conglomerate contain an abundant Chemung fauna, and are considered to be of 

 Chemung age. The first Carboniferous life forms appear with the incoming of the 

 Wolf Creek conglomerate, and from this point up to practically the base of the 

 Olean conglomerate at Olean Rock City, where the last Devonian forms disappear, 

 there is a mingling of Devonian and Carboniferous forms, the Devonian slowly de- 

 creasing, the Carboniferous slowly increasing. The essential fact, so far as the life 

 of these Cattaraugus and Oswayo formations is concerned, is that there is an over 

 lapping of Devonian and Carboniferous faunas. With this essential foct recognized, 



