DALE OWEN ON THE WESTERN STATES OF NORTH AMERICA. 443 



long), C, vermiculare, and other undetermined species ; Stromato- 

 pora and Syringopora ; shells are rare in this stratum ; and several 

 Trilobites, including Calymene bufo and two or three undetermined 

 species of Calymene and Asaphus. 



These coralline strata rest on the ' Catenipora strata' of Clapp, 

 characterized by Catenipora esckuroides, and many of the other 

 Iowa fossils already enumerated ; also Calymene senaria^ Conrad. 



These rocks are best seen at Utica and Charleston landing, Clarke 

 county, Indiana, the upper part only being visible on the Falls. 



In the lower 100 feet of this group in Indiana there are not many 

 fossils ; the only one worthy of note is a coralline resembling a 

 Favosites, but having star-shaped cells ; it is known by the name 

 of AstrcEa favosites. 



The above list of organic remains supplies proof hardly contest- 

 able, that the rocks in which they occur are the equivalents of the 

 " Wenlock formation " of Murchison, some of the Eifel rocks in 

 Germany, those of Drummond Island, Lake Huron, and the Lock- 

 port. Niagara, and perhaps some of the Helderberg limestones of 

 the state of New York. 



The rich and important lead-mines of Iowa and Wisconsin occur 

 in the lower 300 feet of the group I am now describing ; they have 

 yielded more lead than any other formation in the United States, 

 and may be considered hardly second in productive capability to the 

 lead regions of northern England. (See Report, ante cit. p. 37.) 



The lead ore is remarkably free from adhering rock or spar, and 

 is chiefly a very pure sulphuret ; but the compact carbonate is not 

 uncommon, and accompanying them are both sulphuret and car- 

 bonate of zinc in great abundance, and a very rich hydrated di-car- 

 bonate and sulphuret of copper, yielding by analysis from twenty- 

 five to forty per cent, of pure copper. 



The principal vein-stone of these mines is calcareous spar, while 

 at a few localities sulphate of barytes also occurs. The ore occurs 

 in fissures traversing the rock from east to west, rarely from north 

 to south. 



The most characteristic fossil of the true lead-bearing strata is 

 the Coscinopora. The species from Iowa previously enumerated lie 

 about 200 feet above the richest lead veins. 



Hydrated brown oxide of iron is abundant in some localities in 

 the upper 100 feet of the Iowa formation. 



Some of the beds of magnesian limestones of Iowa will yield one 

 of the most durable building-stones in the West : they are objec- 

 tionable only on account of their hardness ; but this is in a niea- 

 sure compensated by the great regularity of the blocks as they 

 come out of the quarry. 



Next in order follow the thin beds of shell limestone, alternating 

 with marl and marlstone : these are the lowest rocks visible west 

 of the Cumberland mountains and south of the Mekoqueta river in 

 Iowa. 



This shell limestone is usually of different shades of bluish grey ; 

 it rings when struck with a hanmier, its fracture is conchoidal, and 



