24 



GEOLOGY. 



group of minerals common in terrestrial igneous rocks, viz., quartz, 

 orthoclase, the acid plagioclases, the micas, the amphiboles, leucite and 

 nephelite, the presence of certain unstable chlorides, sulphides, and 

 phosphides unknown in the earth, and the presence of volatile and 

 combustible hydrocarbons. 



The bearing of these characters. — These make up a remarkable 

 group of characters, whose origin can only spring from an equally 

 peculiar combination of conditions. 



While the fragmental condition of many meteorites, on reaching 



Fig. 1. Fig. 2. 



Figs. 1 and 2. — A meteorite of exceptionally symmetrical form and smooth surface; 

 one of the very few whose external form suggests a possible accretion in free space, 

 and here introduced on that account. The truncated crystals of the cross-section, 

 Fig. 2, however, show that it is reduced from a larger mass of unknown form. The 

 coarseness of the nickel-iron crystals and their arrangement give no suggestion 

 that the mass grew by accretion from a central nucleus. The Boogaldi (nickel- 

 iron) meteorite, 3X5 inches. New South Wales. (After A. Liversidge.) 



the earth, is due to fracturing in their passage through the air, there 

 are indications that they already had a fragmental form when they 



