Relations of Trap-Rocks with Ores of Copper. 299 



normal, all the others are rare, and occur towards the 

 line of contact. Thus the spilites and amygdaloids, with 

 nodules of zeolite or calcareous spar, are only found at the 

 edges of the trap accumulations, when they often form small 

 hills, or particular pitons^ in the same manner as the eupho- 

 tides and the melaphyrcs. When we compare them with the 

 porphyritic rocks, we cannot fail to be struck with the ab- 

 sence of quartz ; the fibrous quartz of Italy is very rare ; the 

 agates and resinous quartz of Oberstein, &c., belong to rocks 

 of contact. The rarity of felspar, which, along with quartz, 

 had hitherto been the dominating principle in the eruptive 

 rocks, is a fact not less interesting; and it worthy of re- 

 mark that the jades and labradors, which are the only acci- 

 dental felspars in the trappean groups, are the least silicated 

 of this mineral family. 



Certain rare substances, such as apophyllite, datholite, 

 prehnite, «&c., are found in some trap groups, very distant 

 from each other, with a remarkable similarity in the circum- 

 stances of their position. These minerals, for example, are 

 found in small contemporaneous veins, and in crystalline 

 g codes, — 



1^/, In the traps of Kewena-Point and the southern shores 

 of Lake Superior, in North America. 



2dy In the traps of Hindostan, at Pounah, &;c., in Asia. 



3</, In the greenstone of the Harz, at Andreasberg, &c., in 

 Europe. 



On studying collections, we cannot fail to be struck with 

 the identity presented by trap specimens from the most re- 

 mote provinces. If, however, we examine the relations of 

 the trappean rocks with the ores of copper and iron, we will 

 find identities much more remarkable and important, in the 

 nature of the ores, and in the circumstances of their position 

 (^gisemeni). 



The metalliferous repositories, with the exception of the 

 vein-fissures, are almost always in relation with the eruptive 

 rocks, a relation of contact, vicinity, and parallelism, and 

 in certain cases of mutual penetration ; so that ores really 

 exist whose origin is eruptive. The facts relating to these 



