532 



HISTORICAL GEOLOGY. 



Virgiuia has been sustained by the discovery, in 1892, of Crinoids, by X. H. 

 Darton, in the slate quarries of Arvon, Buckingham County, Va. A figure 

 of one of the species is here given from Darton's paper. Walcott states 



that the species are allied to those of the genera 

 ScJiizocrijius, Heterocrinus, and Poteriocrinus, 

 and are of either Trenton or Hudson age. It 

 will be seen on a map that the Westchester 

 belt and the Buckingham County locality are 

 so related in position that the latter may have 

 been a part of a long Westchester Taconic 

 Kange, which passed just west of Philadelphia 

 and Baltimore, and may have included South 

 Mountain, Pa., and other ridges beyond, to the 

 east of the protaxis, — the Appalachian Kange 

 being to the west of the same. This would 

 make the Taconic Range of western New Eng- 

 land one in a great Taconic system of mountain 



r 



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;/ 





/^ 



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ranges. 



Crinofd from the crystalline slates of 

 Buckingham County, Va. Darton, '92. 



Eruptive rocks. — Rocks that came up melted, 

 probably at the time of the Taconic disturbance, 

 exist south of Peekskill, N.Y., spread widely 

 over much of Cortland County, and also occur 

 on Stony Point on the opposite (west) side of 

 the Hudson River, The rocks cut through 

 Lower Silurian limestones, and hence are not 

 of earlier ejection ; but they may be of much 

 later origin. They are rocks of unusual kinds, 

 being noryte, chrysolitic hornblendyte and pyroxenyte, coarse dioryte, and 

 a granite-like rock in which the feldspar is oligoclase. The rocks were 

 described by the author in 1880, 1881, and by G. H. Williams in 1886. The 

 long strips of schist and limestone in the igneous rocks appear to prove, as 

 the author stated in his paper, that these eruptive rocks are partly or wholly 

 metamorphic-igneous, produced by the fusion of Cambrian or Lower Silurian 

 rocks during the period of upturning and metamorphism. A dike cutting 

 through the Hudson beds of the Blue Mountains, of west iSTew Jersey, near 

 Beemerville, is probably of the same age. The Beemerville rock also is a 

 rare kind — an Eleeolite-syenyte (B. K. Emerson, 1882). Many ''trap dikes" 

 cut through the Taconic formation in the vicinity of Lake Cham plain which 

 may be of cotemporaneous origin (Kemp and Masters, 1893). 



The Cincinnati geanticline. — Cotemporaneously with the disturbances 

 above described the low geanticline was formed, called the Gincinnati iqylift 

 (page 537). making two islands, one over part of Ohio, eastern Indiana and 

 Kentucky, and the other over Tennessee, as reported by Saiford, Newberry, 

 and Orton. The general course of the upward bend of the crust was north- 



