438 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



but I have found (besides the one above alluded to) several indivi- 

 duals of a small species of Calymene. ProductcE and Terebratulce 

 are abundant in these rocks. It appears therefore from this com- 

 parison of the fossils, that these limestones are the equivalent of the 

 carboniferous limestone of Europe. 



At the junction of the coal-measures and these limestones occur 

 valuable deposits of iron ore. In many localities in Indiana I have 

 discovered extensive deposits of hydrated brown oxide of iron in this 

 geological position ; and Dr. Hildreth describes, in the American 

 Journal of Science for October 1835, a " Great Ferruginous Depo- 

 sit" bordering south-westerly and northerly on the main coal-mea- 

 sures of Ohio. 



Some of the best building-stones in Indiana are from quarries in 

 these limestones. Most of the beds afford lime almost as white as 

 magnesia, forming a striking contrast to that made from limestones 

 of the coal-measuresj which is usually of a dark brown colour. 



In the southern part of Illinois, thirty or forty miles west of Shaw- 

 neetown, these limestones are traversed by small veins of galena, 

 associated with fluate of lime and sulphate of barytes. This lead 

 ore has been explored to some extent, but the quantity hitherto ob- 

 tained has not proved sufficient to render mining in this vicinity 

 profitable. Many have been induced to work this lead ore, on the 

 supposition that it contains a large per-centage of silver, but the spe- 

 cimens that I have been able to obtain and analyse have not yielded 

 more than one per cent, of that metal. By far the finest specimens 

 of fluor spar in these Western States have also been obtained in this 

 locality ; some of it crystallized in cubes, the prevailing form, and 

 some of it compact. On a branch of Grand Pierre Creek I noticed 

 a vein of compact fluor spar eighteen inches thick, running across 

 the bed of that stream in a north-easterly course. 



On the west slope of the Cumberland mountains the geologist of 

 Tennessee discovered in the bed of a small stream (Calf-killer Creek) 

 a specimen of sulphuret of silver penetrated by crystallized fluate of 

 lime ; and another person obtained, near the same spot, a small frag- 

 ment of sulphuret of silver in combination with sulphuret of lead. 



Dr. Troost does not decide where these ores have originated, not 

 having noticed metallic veins in rocks of this vicinity. But as the 

 above stream flows over limestones belonging to the group under 

 consideration, and since these are traversed in Illinois, as we have 

 seen, by veins of galena and fluor spar, I conclude that these mine- 

 rals may have originated in this limestone formation. I believe no 

 rocks of a similar nature and age have been observed in the At- 

 lantic States. 



The rocks which succeed to the Pentremital limestones are those 

 coloured yellow on the map. Their lithological character is usually 

 that of grey or yellow and brown sandstone ; soft, fine-grained and 

 siliceous ; sometimes argillaceous and free from mica. These sand- 

 stones pass, on the one hand, into chert and hornstone, and on the 

 other, into a rock possessing the appearance of tripoli. Interstrati- 

 fied with these argillo-siliceous deposits are beds of limestone, sel- 



