Ries — Geology of Orange County. 



419 



Whitfield, who identified them as upper Silurian, and recognized the species 

 Spirifrr cyclopterus, Spirifer macropkwus and Orthis ohlata. 



An actual contact of the limestone and quartzite is not visible, but the 

 former passes unconformably under the latter. The relations of these two are 

 probably those of an overthrust or overlap, as explained by Darton.* 



The Helderberg limestone overlies the Cambrian limestone unconform- 

 ably. The latter outcrops along a cross-road (440) just east of Bull hill, and 

 a few hundred feet to the northeast of the Helderberg exposures. It is in 

 thin shah' layers, which are seamed by numerous hair-like calcite veins. The 

 rock is also full of cavities containing powdery limonite. In places the lime- 

 stone is porous and nearly as light as wood, owing to the leaching out of the 

 lime. It also, at times, presents a brecciated structure. The strike is 

 N. 80° E., and the dip 30° S. The Cambrian limestone appears again at the 

 eastern base of Bull hill, near the southeast end, in the railroad cut at the 

 south end of the ridge, on its western slope, and on the northwestern side. It 

 presents variable dips and strikes, and overlies the gneiss of Bull hill uncon- 

 formably, at least on the eastern and southern side of the ridge, but on the 

 western slope the limestone is overlapped by the Hudson river slates, which 

 rest unconformably on the western slope of the gneiss. The relations of the 

 rocks of the small area are shown in figure 6. 



The Oriskany quartzite seen east of Bull hill, probably extends to the 

 north, but is obscured by the heavy covering of drift to a point about one- 

 half mile south of Round hill, where there is a small area resting on the 

 gneiss. It next appears in the eastern slope and summit of a ridge between 

 Round hill and Woodcock hill, again exhibiting the conglomerate facies, 

 with an occasional layer of coarse sandy quartzite. The strike on the crest of 

 the ridge (242) is N. 60° E., dip 30 to 40° S. The Hudson river slates form 

 the western half of this ridge, extending to and along the southern base of 

 Woodcock hill, where the stream has cut a deep gorge through them (245). 

 A short distance southeast of this point, and along the road crossing the south 

 end of Woodcock hill (246), the Cambrian limestone appears. It is light 

 blue, finely crystalline, and contains many calcite veins. It strikes N. 50° W., 

 and dips 30° K E. 



The quartzite is again seen at the edge of a small wood, south of the 

 same road (247). It is here a coarse conglomerate, with a strike of N. 40° E., 

 and a dip of 50° S. E. The limestone is seen just west of it, and underlies it 

 with a slight unconformity, dipping 60° S. E. The limestone also appears at 



* Bulletin Geological Society of America. V , p. 367. 



