BIGSBY PALEOZOIC ROCKS OF NEW YORK. 341 



Fossils. — See General Table, No. I. 



We have here many marine plants — parts of large, succulent, 

 hollow stems. Shells mostly univalves. Fossils apparently few ; 

 but they were in reality many, but have been obscured by siliceous 

 infiltration and by physical disturbances (Hall, Pal. i. 9). The 

 upper half is the most fossiliferous. Emmons (Report, p. 114) 

 remarks that, thin as are the subordinate masses of this rock (15- 

 30 ft. only), yet each has its own typical fossils. Also, the species 

 are few, forms peculiar, and individuals numerous. 



Fossils typical. — Palseophycus tubulosus ; P. irregularis; Buthotrephis 

 antiqua; Lingula acuminata; Euomphalus uniangulatus ; Ophileta levata; 

 O. complanata ; Maclurea matutina ; M. labiata ; M. sordida ; M. 

 striata; Turbo diluculus; T. obscurus ; Pleurotomaria turgida; Bellero- 

 phon sulcatus ; Orthoceras laqueatum ; O. laq. var. a ; O. primigenium 

 (Vanux.). 



Fossils occurrent in Europe. — Orthoceras laqueatum ; Bellerophon sul- 

 catinus. 



Fossils recurrent in New York. — Scalites angulatus. 



Chazy or Black River Limestone. 



Mineral Character. — This rock is well defined. It is grey, blue, 

 very compact or subcrystalline, and in layers which are never more 

 than 10 feet thick. There are cherty masses occasionally. 



Transition. — This is gradual, below and above. Vanuxem unites 

 Chazy Limestone with the next, the Birdseye Limestone. They 

 are often undistinguishable, especially on the River Madawaska in 

 the Ottawa Valley, U.C. 



Place. — Its position is well marked at Chazy Village, on the west 

 side of Lake Champlain. Hall says it is very persistent, and is 

 known almost across North America, but only in patches of moderate 

 size, as in the valleys of the Mohawk and of the Black River, hidden 

 or brought into view by the contours of the country. The latter 

 river has given a name to the rock (Emmons, Report, p. 107). It 

 is plentiful in Canada. 



Position. — It has a moderate dip to the west, near Essex, on the 

 west side of Lake Champlain. The inclination is to the south and 

 west, and slight elsewhere, except near dykes and uplifts on Lake 

 Champlain. 



Thickness. — This is 130 feet, including Birdseye Limestone, to 

 the west and south of Lake Champlain. 



Fossils. — See General Table. 



This period was more favourable to animal life than some subsequent 

 ones. Forms here obscure become numerous and prominent at suc- 

 ceeding periods. Swarms arose of crinoids and zoophytes in the 

 earlier parts of the period, with crowds as multitudinous of Brachio- 

 poda and Cephalopoda in other parts, and especially of Maclurea (Hall, 

 Pal. i. 15). There are eight (?) species of Trilobites ; but individuals 

 are few. Nearly every species perished at the end of this period. 

 Scarcely one of the Orthocerata of Chazy Limestone is known to 

 ascend into any subsequent deposition. Of the peculiar forms which 



