KEMAINS SHELLS. 



417 



polish. Fluor-spars occur abundantly in veins in the vicinity 

 of Castleton, and the manufacture of this substance into 

 cups, vases, &c., constitutes a local branch of industry of 

 considerable importance. Manganese, copper, zinc, barytes, 

 and iron, also exist in this formation ; but the most abundant 

 ore is the sulphuret of lead or galena, of which there are 

 several extensive mines. 



OKUANIC REMAINS. These consist of an abundance of 

 corals, chiefly of the genera which form coral reefs : there 



FIG. 299. Bellerophon cornu-arietis. 2. Prodncta scabricnla. 3. Spirifera 

 trigonalis. 4. Producta punctata. 6. Orthoceras uqdatum. 



are also great numbers of crinoidea, the debris of which 

 make up extensive beds of limestone. Of the conchiferous 

 mollusca the prevailing genera are Spirifera and Producta. 

 Of cephalopoda, the prevalent genera are Orthoceras, Gonia- 

 tites, and Nautilus. The Orthoceras was a chambered shell, 

 like a nautilus, but uncoiled and straight: the Goniatites 

 have the borders of the septa free from denticulations. The 

 JSuomphalus is an extinct genus of univalves, extremely 

 abundant in this limestone. The interior is often. divide*d 

 by septa, but the partitions of these chambers are not 



