76 



OUTLINES OF GEOLOGY. 



ORDER IV. OPHIOLITIC. 



175. The rocks of this order are as follows : 



1. Serpentine; 



2. Ophicdlce, a mixture of serpentine with carbonate 

 of lime, and which, when the former preponderates, and the 

 carbonate occurs in veins, is known as verde antique marble ; 



3. EupJiotide, composed of diallage and felspar ; 



4. Magnesite, a silicitate of magnesia ; 



5. Granular dolomite. 



176. The serpentine rocks are traversed by many veins, 

 and with the others contain numerous imbedded minerals. — 

 Of those which occur in these different modes the most im- 

 portant are : 



Hydrate of magnesia, Idocrase, 

 Carbonate of do. Felspar, 

 Hornblende, Asbestus, 

 Sahlite, Crysoprase, 

 Oxide of chrome, Chromate of iron, 



Manganese, Magnetic iron. 



177. The vicinity of New- York presents two interesting 

 localities of this order, at Hoboken, and on Staten Island. 

 It is from observation of these localities that, in opposition to 

 other authorities, it is stated that the serpentine rocks are 

 traversed by many veins. On the island of New-York and 

 on the bank of the Hudson, at Anthony's Nose, serpentine is 

 associated with gneiss and mica slate ; the lower limit of this 

 order is therefore the latter rock. Brogniart states that its 

 upper limit is unknown. It probably does not ascend very 

 high ; at any rate, the rock of Hoboken is older than the 

 adjacent sand-stone. 



