306 Darton and Keith — Dikes of Felsophyre and 



center of Appalachian uplift which in the Crabbottom valley 

 west of Monterey attains unusually great altitude. 



The distribution of the rocks of each of the two principal 

 varieties is shown in Fig. 1. 



The basaltic rocks at Nos. 1, 2, 3, 4 and 6 were described in 

 the publication above referred to. They are all small dikes, 

 Nos. 2 and 4 cutting Lewistown (Heldersberg) limestone, and 

 No. 5 rising at the contact of Romney shale (Marcellus) and 

 Monterey (Oriskany) sandstone. Nos*. 4 and 5 are associated 

 with friction breccias composed of a variety of more or less 

 altered sedimentary rocks. The other dikes of basalt discovered 

 in 1896 are of similar character but some of them are of larger 

 size. The outcrop No. 16 at Sounding Knob is on the top of 

 a high anticlinal mountain of Tuscarora (Medina-Oneida) quart- 

 zite, the igneous rock rising as a steep-sided neck about 80 feet 

 above the crest line. The altitude of its summit is nearly 4,500 

 feet. The outcrop No. 9 is a dike which extends down the 

 west side of Monterey mountain in the great Crabbottom anti- 

 cline cutting through Martinsburg (Hudson) shale and Shenan- 

 doah (Lower Ordovician-Cambrian) limestones. Its width 

 varies from 30 to 120 feet and its course is nearly due north- 

 west. The dikes Nos. 13, 14, and 15 are along probably one 

 line of intrusion trending northeast, but they appear not to be 

 connected at the surface. At No. 15 there are showings of 

 friction breccia of somewhat altered sedimentary rocks. 



The acid rocks have only been observed within a radius of a 

 few miles from Monterey. The dikes are small and inconspic- 

 uous. The best exposure is on. the upper forks of Straight 

 Creek, three miles east-northeast of Monterey. Here the rock 

 occurs in several large white masses rising in a low knoll with 

 an area of only a few square yards. The material is hard, fresh, 

 and very characteristic. A few rods south at No. 5 there is an 

 exposure of basalt, and a short distance west are two small 

 exposures of narrow dikes of the weathered acid rock. They 

 are all in Rockwood (Clinton) shales. The relations of the 

 rocks to one another in these exposures could not be determined, 

 owing to lack of continuity of outcrops. Near the mouth of 

 Straight Creek, at No. 15, there is a small exposure of the acid 

 rock cutting the Monterey sandstone. The dike near Mon- 

 terey, No. 20, is exposed along the roadside about a half mile 

 northeast of the village cutting Romney shales. It can only 

 be traced for a few yards. In the Crabbottom valley three 

 exposures were discovered, at Nos. 21, 22, and 23, in the She- 

 nandoah limestone along the road from High town to New 

 Hampton. A half mile north of Hightown, at No. 21, two 

 small dikes of decomposed and weathered felsophyre are seen 

 in the roadcuts penetrating Shenandoah limestone. At Nos. 

 22 and 23 several other small dikes are exposed. They are 



