MINERALOGY. 407 



It contains the fossil remains of mollusks in great num- 

 bers and variety.* 



THE JURA FORMATION. 



The assemblage of sedimentary rocks, to Avhich has 

 been given the name of the Jurassic Formation, com- 

 pose the foundations of the Swiss and Suabian Alps, 

 and form the most remarkable strata of the Jura. The 

 first of these layers which claims our observation is the 

 calcareous matter or structure called coral chalk, or coral 

 rag, which is a great porous net-work, composed of coral- 

 lifercB, which belonged to an antediluvian Avorld, and are 

 remarkable as forming numerous cavernous fissures or 

 structures, which often contain mineral treasures. We 

 shall mention a few of the most important.! 



Bohn-ertz Bog Iron Ore Limonite, a loose, earthy 

 ore ; is found in veins, or arched beds, and often repre- 

 sents large globular masses, containing, although mixed 

 with much silicious earth, two-thirds its own weight of 

 pure iron. Occurs connected with rocks of all ages, but 

 is mostly found below the tertiary rocks ; however, in 

 many parts of the Suabian Alps it lies so closely beneath 

 the upper surface as scarcely to be concealed. 



Oolite, also called Roestone, because it is composed 

 of small globules resembling the roe of fishes, is of a 

 light brown or whitish-ochery color, seldom gray, but 

 sometimes blue ; a variety of common limestone, usually 

 found in the conformable position of strong stratifications, 



* The greatest deposit of Gypsum is that of Paris, and extends 

 twenty leagues. It is noticed as singular that, throughout the extent 

 of the two Americas, not a specimen of chalk has been found. 



f See Macculloch on Coral Formations, vol. i. 33*7. 



