DEVONIAX AND CARBOXIFEKOtJS IX XEW YORK 527 



upper surface of the Cattaraugus is irregular because of erosion, and that there is 

 an unconformity between the Cattaraugus and the succeeding Oswayo. 



Composition. — The close of the Cattaraugus was marked by the cessation of the 

 deposition of red shales in this region. After what is believed to have been an ero- 

 sion interval it was followed by the deposition of olive green to rusty colored sandy 

 shales, with here and there thin sandstone layers with limonitic seams or incrusta- 

 tions. These greenish, limonitic shales constitute the Oswayo formation. Its 

 thickness varies from 160 to 250 feet, the average being near the latter number. 

 Conditions now became more favorable to the existence of life, and, in contrast to 

 the usual barrenness of the red shales below, the Oswayo contains in many places 

 a fairly good representation of marine invertebrates, prominent among which is 

 Camaroioechia allegania, w^hich serves as an excellent horizon marker. 



Limestone layer. — A few feet above the base of the Oswayo shale is found in a 

 number of places in New York what seems to be a persistent layer of very impure 

 limestone. It is only 1 or 2 feet thick and the entire stratum is composed of innu- 

 merable fragments of badly broken brachiopod and other marine shells. 



Near the top of the Oswayo, on the Clean quadrangle, the shales become sandier, 

 and at Clean Rock City there are some traces of thin grits about 40 feet below the 

 base of the Clean. Nowhere on this quadrangle, however, have such gritty beds 

 been found exposed in place, and at several points good exposures of this part of 

 the section are to be seen — as, for instance, on the road from Fourmile down into 

 Fourmile Creek valley. 



KXAPP FORMATION 



On the Salamanca quadrangle there are found beneath the Olean conglomerate 

 two thin conglomerates interbedded with shales that are lithologically very simi- 

 lar to the underlying Oswayo shales. These are doubtless, in part at least, the 

 equivalents of the grits and shales just beneath the Olean at Rock City and which 

 are included in the Oswayo there, but which evidently thicken and coarsen west- 

 ward until they are capable of differentiation as the Knapp formation. These 

 beds are not usually well developed on the Salamanca quadrangle, and have been 

 found in only a few areas along the southern edge. South w^est ward in Pennsyl- 

 vania a more prominent conglomerate, known as the Sub-Clean, is situated in a 

 similar stratigraphic position beneath the Olean, from which it is separated by 

 from 25 to 30 feet of shales. It is known over a large area and extends, according 

 to the Pennsylvania geologists, w^estward into Ohio, where it is known as the 

 Shenango conglomerate. It, with the associated Shenango shales, is probably the 

 equivalent of this Knapp formation. 



The coarser part of this formation is usually a loosely cemented conglomerate 

 with small, well smoothed quartz pebbles of flattened discoidal shape that only in 

 places becomes massive. It is frequently highly limonitic, and in most places 

 where examined was fossiliferous. The fossils consist of marine invertebrates and 

 plant stems of various kinds. The shales are sandy and olive green or rusty 

 brown and in several places contain marine invertebrates. 



In places these beds have been cut out by erosion before the deposition of the 

 Olean conglomerate — as, for instance, on the ridge north of the head of Irish 

 brook, where Olean caps the hill — but with no sign of an underlying conglomerate 



LXXIII— Bull. Geol. Soc. Am., Vol. 14, 1903 



