1869.] Mineralogy. 137 



hensive treatises, it is our duty to call attention to a useful little 

 work recently written by Dr. Kenngott, of Zurich.* 



Those who are unable to wacle through the larger volumes will 

 here find an excellent outline of modern petrography. In the early 

 chapters the author gives as much elementary mineralogy as he 

 considers needful as an introduction to petrology. When we re- 

 member that it is to the want of miueralogical training on the part 

 of most geologists that the backward state of petrology must mainly 

 be referred, the propriety of such an introduction is at once evident. 

 A chapter then follows on the general relations of rocks, in which 

 are discussed their miueralogical constitution, physical structure, 

 and j)robable mode of original formation and subsequent alteration. 

 The writer then j^roceeds with the systematic description of the 

 different sjjecies of rocks, and, without any pretence to origmahty, 

 goes over much the same ground as is usually covered by the larger 

 treatises. It should be remarked that in expressing symbohcaUy 

 the chemical constitution of rock-forming minerals, he introduces 

 the new atomic weights, whilst he retains the old method of rational 

 formulas. The propriety of this seems questionable. Good geo- 

 logists are, as a rule, bad chemists ; and much confusion may there- 

 fore arise on comparing Kenngott's formulae with those given in 

 other miueralogical works. In dismissing the book, it is only neces- 

 sary to notice its unusually full index — an index which in some 

 measure plays the part of a sup^^lement, inasmuch as it contains 

 short descriptions of unimportant rocks which find no place in the 

 body of the work. 



Whilst Germany, without doubt, takes the lead in petrological 

 science, France occupies a position far from discreditable, as amply 

 testified by the writings of such men as Daubree, Durocher, Coquand, 

 and Delesse. Among her most ardent students must be numbered 

 the late M. Cordier, who for more than a quarter of a century 

 devoted himself to the study of rocks. At once an accomphshed 

 mineralogist and an experienced traveller, Cordier was well fitted to 

 examine his sj)ecimens by the most minute and exact methods, while 

 he was kept from those narrow generalizations in which the mere 

 worker in the cabinet is too prone to indulge. His collection of rocks, 

 now deposited in the Geological Gallery of the Museum of Natural 

 History in Paris, numbers no fewer than ten thousand specimens, 

 each said to represent a distinct variety ! To classify this myriad of 

 specimens with scientific acciu'acy was the great end of Cordier 's life. 

 Although miueralogical composition was the leading feature of his 

 system, he was far from relying solely on any single characteristic — 

 whether chemical, physical, mineralogical, geological, or genetic — 



* ' Elemente der Petrographie, zum Gebrauche bei Vorlesungon und zum 

 Selbststudium, bearbeitet von Dr. Adolf KenDgott.' 8vo. Leijizig, 18G8., pp. 274. 



