LOWER SILURIAN. 185 



The reference of part, at least, of the Stockbridge limestone formation of the Green 

 Mountain region, to the Chazy, is based on the discovery of fossils in West Rutland, 

 by Rev. A. Wing, as described by Billings. The latter states that he identified a Cri- 

 noidal plate as pertaining to Palceocystites tenuiradiatus, a characteristic Chazy species, 

 and a Mollusk as Pleurotomaria s/amineaDn. 



The rocks supposed to be equivalents of the Chazy in the Mississippi basin are 

 mentioned on the preceding page. A limestone of the age has been stated to occur in 

 the Winnipeg region, west of the Archsan. 



(C.) Appalachian region. — The Chazy has not been distinguished from the Trenton 

 in the Green Mountains, or in Pennsylvania; in the latter State, there is a magnesian 

 limestone, according to H. D. Rogers. 



In East Tennessee, it is represented by from 50 to GOO feet of blue and drab, more 

 or less concretionary, argillaceous limestone ("Maclurea limestone " of Safford). 



{d.) Arctic region. — Limestone strata, containing Chazy fossils, have been observed 

 in the Arctic, on King William's Island, North Devon, and at Depot Bay in Bellot's 

 Strait (lat. 72°, long. 94°). The species Orthoceras moniliforme Hall and a Maclurea 

 (M. Arctica Haughton, near M. magna), have been observed. The limestone is in 

 part a cream-colored dolomyte. 



Igneous or Intrusive Rocks. 



Through New York and the States directly West, no evidences of 

 disturbance have been observed that can be traced to this period. 

 The rocks are for the most part nearly horizontal, and in general 

 little altered ; and the tilting which is observed appears to have taken 

 place at a later period. But, on Keweenaw Point, the famous copper- 

 region of Lake Superior, the sandstones of this period are associated 

 with trap, — an igneous rock, that was ejected through fissures opened 

 in the earth's crust ; and these trap ejections have added much to 

 the accumulations. Some of the conglomerate (according to Foster 

 and Whitney, and Owen) seems to be made of volcanic scoria, like 

 the tufa of modern volcanoes, as if the ejections had been submarine, 

 and the cool waters had shattered the hot rock to fragments, and so 

 made the material of the conglomerate ; and, as many of the masses 

 are not rounded, these authors infer that it was piled up rapidly 

 during the igneous action. Dr. D. D. Owen represents the trap as 

 often in layers, alternating with shale and other rocks, indicating 

 eruptions at different times. The traj) rocks of Lake Superior present 

 many scenes of basaltic columns of remarkable grandeur. Some of 

 them are represented and described in the Geological Report on Wis- 

 consin, Iowa, and Minnesota, by Dr. Owen. The native copper of 

 the Lake Superior region is intimately connected in origin with the 

 history of the trap and sandstone. 



II. Economical Products. 



Copper mines are numerous in the rocks referred to this period, 

 and many of them are highly productive. Those of Keweenaw Point, 

 on the southern border of Lake Superior, are among the most remark- 



