418 



Report of the State Geologist. 



difficulty. The nodules have a shell which resembles the sandstones into 

 which the nodular rock shades. A section of this nodular rock show s it to 

 be a portion of the sandstone which is firmly cemented with iron. 



The structure of Pea hill is probably that of a synclinal fold. The 

 Monroe shales are underlaid by the Oriskany quartzite which, in Pea hill, is a 

 coarse pebbly quartzite, massively bedded and very hard. There are good 

 exposures of it along the road at the northeast side of Pea hill, where these 

 fossils were found : 



Anoplia nucleate/, 



Stropheodonta, sp.? 



Leptoena rh om baidalis, 



Leptoeoelia fa bellites. 



The Hudson river slates no doubt form the bottom of this synclinal 

 fold, but outcrops are lacking in the immediate vicinity. 



The general structure of Sknnneniunk mountain is that of a much more 

 open synclinal than Bellvale mountain to the southwest. But at the northern 

 end, the flags and sandstones of the eastern limb turn over and downwards 

 on to the limestones of the Helderberg and Cambrian, as already shown by 

 Darton. 



The Relations along the Northwest Side of Skunnemunk Mountain. 



The Oriskany quartzite, which forms the ridge along the west side of 

 Seely's brook, southwest of Oxford, turns to the east, cropping out in the 

 field below the road, half a mile south of Oxford station (144). At this 

 locality, it is both coarse-grained and finely granular. The next outcrops are 

 in a field about one mile due east of Oxford and west of the high-road. There 

 are three small outcrops, which are hard reddish quartzite with white seams 

 of quartz. Farther east, on Bull hill, are two small areas of the same for- 

 mation of a more conglomeratic nature, and which rest on the Hudson river 

 slates. They strike N. 40° W., and dip 55° N. E. This locality east of Bull 

 hill is of considerable importance as affording an explanation of the strati- 

 graphic relations of the rocks in this region. The quartzite area (489) is 

 underlaid by a thin-bedded, shaly, dark grey limestone striking N. 60° E., 

 dipping 35° S. E. In the limestones are numerous fragmentary remains of 

 bryozoans, crinoid steins and corals, all of them too poorly preserved for 

 identification. On examination of the specimens Professor Hall pronounced 

 them to be Lower Tentaculite limestone. Some years ago, N. II. Darton 

 submitted some specimens from the same locality to Professors Hall and 



