l INTRODUCTION. 



serpentine. The nucleus of the earth, as he observes, must 

 be chiefly ferruginous, as is not only announced by the gene- 

 ral phenomena of magnetism, but by the observations and 

 experiments of Maskelyne and Cavendish, which show that 

 the specific weight doubles that of rock crystal*. 



In his mineralogy, Patrin begins with a description of the 

 primitive rocks, which he introduces by that of the chief 

 substances of which they are composed, . namely, quartz, 

 felspar, mica, and schorl. This last term is generally used 

 by the French geologists for siderite or hornblende. ' ( Often," 

 says Patrin, " it forms considerable masses of rock, and 

 even entire mountains. When the schorl- rock presents a 

 distinct laminar texture, it is called hornblende ; when the 

 texture is of an earthy appearance, it is named Corneene" 

 This last word is often used by the French for basaltin. 

 Thus, in the opinion of this great observer, who has passed 

 many years in the mountains of Siberia, schorl or horn- 

 blende, composed of siderous earth, is as primitive as any of 

 the rocksf. 



Magnetism. But while these great geologists admit the ferruginous or 

 siderous among the principal earths, they seem never to have 

 connected this idea with that of most writers on magnetism; 

 who, in order to explain that phenomenon, are forced to 

 admit that the nucleus of this our planet is a mass of iron : 

 and as, according to all theories, the substance which is 

 nearest the centre must be the most ancient, of course the 

 siderous earth must often partake of this antiquity; and in- 

 stead of ranking it, with Dolomieu, in the third or fourth 

 succession, it may be more properly classed in the first. In 

 the mica of granite, and often in the felspar, and even in the 

 quartz, a portion of iron is discoverable : and basalt, which 

 ^ contains a large portion of iron, is sometimes intermixed 



* Min. v. 11, 4$, 241. The mountains of Selinga, he says, are chiefly of 

 hornschieffer and hornblende. 



f Siderite and schorl shoot across quartz and felspar, so are more ancient : 

 so siderite and basalt intersect granite. 



