DETAILS OF THE SECTIONS 481 



plex type of cross-bedding found in eolian rocks, while the conglomerate 

 beds show the compound oblique bedding characteristic of torrential for- 

 mations. This latter type of cross-bedding Mr. Billingsley found to pre- 

 dominate, being the characteristic type of the formation from bottom to 

 top and from one end of its outcrop to the other. The direction of the 

 oblique layers when corrected for later disturbance is generally to the 

 northwest. The shales are generally sandy and dark colored to black; 

 they are mostly limited to the lower half of the formation, and in several 

 localities, notably at Otisville and the Delaware Water Gap, they have 

 furnished an abundant but extremely fragmentary fauna, consisting 

 chiefly of Eurypterids. The species so far described are Eurypterus 

 maria Clarke, Eusarcus cicerops Clarke, Stylonurus myops Clarke, Stylo- 

 nurus cestrotus Clarke, Stylonurus sp. Dolichopterus otisius Clarke, D. 

 stylonuroides CI. and R., Hughmilleria shawangunk Clarke, Pterygotus 

 globiceps CI. and E., besides fragments referred to Phyllocarida. These 

 remains and their bearing on the general problem of the origin of the 

 formation will be discussed farther on. 



The petrographic character studied at length by Billingsley shows sev- 

 eral interesting features. The pebbles of the formation seem to be nearly 

 all vein quartz, while in point of wear they are not so well rounded as 

 are those of the Oneida conglomerate. Mingled with the sand grains of 

 the matrix there is an abundance of feldspar, much of it in a very nearly 

 unaltered state, so that the rock frequently assumes the characters of an 

 arkose. This is, of course, not found where eolian cross-bedding is well 

 developed, as in an outcrop on the Schuylkill Eiver studied in detail by 

 Billingsley. Here the remarkably fine development of the eolian cross- 

 bedding was accompanied by great purity of the sand, a striking assort- 

 ment of the grains according to size and a great perfection of rounding 

 of the individual grains. On a lithological basis, Billingsley was able to 

 divide the Shawangunk formation into two parts. The lower division 

 comprises coarse conglomerates with intercalated black shales, often 

 carrying Eurypterids and with gray sandstones, showing the presence of 

 carbonaceous particles under the microscope. With this occurs bog iron 

 ore, and the whole series has the aspect of having accumulated under 

 comparatively moist climatic conditions. This portion of the formation 

 disappears in the sections north of Otisville and south of the Lehigh. 

 The second division consists at the base of coarse, white conglomerates 

 and sandstone rich in feldspar and passing upward into rod sandstones 

 and shales. This division overlaps the lower one to the north and south, 

 being the only one present in the Shawangunk Mountains ami northward 

 and on the Schuylkill Water Gap. 



XXXIII— Bull. Gkol. Soc. Am., Vol. 24, 1012 



