HUDSON SHALES. 385 



unquestionable in the Cornwall region, where the Green Pond, Long- 

 wood, Helderberg and other series present the full sequence. In New 

 Jerse}^ there are shales underlying the conglomerate along the east side 

 of Kanouse mountain near its northern end, but it is not as yet demon- 

 strated that they are Hudson in age. 



The estimate of the total thickness by Merrill of 600 feet in the New- 

 foundland region is considerably too great. I find that the 500-foot cliff 

 south of the station, on which his estimate is based, contains nearly 100 

 feet of crystalline rocks at its base, but probably a considerable portion 

 of the original thickness of sandstone was removed from its summit. The 

 formation appears to attain its greatest thickness at this locality, for the 

 average amount is considerabl}^ less elsewhere. 



The name Green Pond Mountain conglomerate or series has been ap- 

 plied to the formation by Cook, Smock and others, and, although origi- 

 nally always used to include the Skunnemunk conglomerate, it is, I 

 believe, an appropriate name, with proper restriction, for the Upper Silu- 

 rian member. The " mountain" may be omitted to advantage, as Green 

 Pond is a tj'pical locality. It is not proposed at present to separate the 

 quartzite under a distinctive name. 



Hudson Shales. — The Hudson shales are overlapped by the several 

 Upper Silurian and Lower Devonian members in Orange county, es- 

 pecially to the north and west. 



The formation consists mainly of gray to brownish graj^ shales, with 

 more or less slaty cleavage. There are some sandy beds, notably, in 

 the vicinity of the lines of sections IV and V, plate 17, which have a 

 2)osition near or at the u])per part of the formation. These sandy beds 

 are light gray in color, semi-quartzitic in composition and give rise to 

 rough, rocky ridges of some prominence. They were found to contain a 

 few Orthis testudinaria near the line of section V. They have been in- 

 cluded with the Oriskany fpiartzite as Oneida and Potsdam by Cook in 

 his 1868 and 1874 maps. 



In 1885 * I had the good fortune to discover fossils in this formation 

 which definitely proved the Hudson river age of the slates. Since 

 theji many new localities of fossils have been noticed. The principal 

 fossils are Leptenx sericia, Orthis testudinaria and 0. plicatella, but there 

 are several others of typical upper Ordovician age. The overlap of 

 Hudson shales on the cr3"stalline rocks is a noteworthy feature in this 

 region, and the small outl3dng Archean areas rise in greater part as 

 " islands " through the shales. 



* PreJimiuary Notes of Fossils in the Hudson Rivei* Slates of the southern Part of Orange County, 

 New York : Am. Jour. Sci., 3<1 ser., vol. xxx, pp. 4.')2-1.5?). 



