RICHTHOFEN'S YIEW8. 275 



from a oareful stuch- and coinparisdu of a large luiinber of clieiuical aiialvsn.s 

 of crystalline rocks gathei-ed from all parts of the woi-ld, differing \videl\' in 

 their raineralogical development and structm-al habit. 



Besides these references to original contributions the reader who <[(- 

 sires to pursue the subject still further will find an excellent sunnnary of 

 the views of Buusen, Durocher, Roth, and others, published by Ferdinand 

 Zirkel in his text-book of petrography.' 



Waitershausen's Conclusion.— Sartorl US vou Waltershausen, after a careful 

 investigation of the lavas of Sicily and Ireland, published the results of his 

 researches in an elaborate memoii- in which he presented his conceptions of 

 the physical condition of the interior of the earth. His conclusions, so fiir 

 as they i-elate directh' tt) subjects considered here, stated briefly, were that 

 between a superfcial cool crust and a solid inteiior there existed a broad 

 belt of fused material of undetermined tliickness which furnished the source 

 of supply for the lavas poured out upon the surface. "^lliis material 

 arranged itself appi-oximately according to its density. The most acid lava, 

 being the lightest, was situated nearest the surface, followed b)- that of 

 intermediate composition characterized bv minerals of somewhat higher 

 specific gravit\ , and tcrniinatiiig liiuilly with the heaviest, and consequently 

 most basic, lavas — basalts — can-yiug large amounts of magnetite and other 

 iron minerals. He concludes that in most instances the lavas were ejected 

 in the order of their po.sition, the lightest being first thrown out, imperfect 

 separation by specific gravity being sufficient to account for all exceptional 

 occurrences. This simple and regular order of succession met nearly all 

 the requirements of Waitershausen's personal observations and were in 

 accord with his theories." 



Richthofen's Views.— Barou \()n Kiclitliofen acccptcd the main conclusions 

 of Waltershausen regarding the physical conditions of the globe, agreeing 

 with him as to the evidences of a liquid mass lying between a solid 

 interior and a superficial outer crust. This liquid mass was acid 

 near the surface, l)asic beneath, with the intermediate transition lavas 

 between them. He traveled extensively in the volcanic regions of Europe 



' Lehrliuoh der Petrographie. Bonn, er.ster Baud, 1866, p)). 453-473. 



-Uelier die vulkanisclien Gesteine in Sicilieu iind Island nnd ihre submaiiin' riiibildiiiig, Giit- 

 tiiigin, 18.o;<. 



