Geology and Natural History. 153 



Mr. Clarence King. Therefore this work from his pen, in his 

 chosen field after so long a silence — the reasons for which he states 

 in the preface — will be without doubt eagerly welcomed and read 

 by American petrographers and geologists. 



The first volume, now issued, treats in the main of methods of 

 petrographical research, the use of the microscope, of polarized 

 light, of methods of separation and microchemical tests. Then 

 follows the microscopical physiography of the more important 

 rock- making minerals, which are treated in detail only in respect 

 to those points which are of immediate petrographical interest. 

 The list of minerals thus made out has been somewhat arbitrarily 

 selected — thus we note that vesuvianite, although common in con- 

 tact metamorphic areas, is omitted, while dumortierite, for exam- 

 ple, is given. No cuts of any kind are introduced, the author 

 stating his reason in the preface for omitting them. 



This portion of the subject occupies about half the volume, the 

 remainder is taken up with general petrography — the various 

 types of structures (comprising really texture as well) of rocks are 

 then given, their general methods of geological form, of alterations 

 by weathering, by contact metamorphism and dynamic forces, etc. 

 Then the igneous rocks are taken up, and treated from a general 

 standpoint, their chemical relations, processes of crystallization, 

 differentiation of magmas, etc , ending with their classification. 

 It would be impossible here to review this part of the work as it 

 deserves: — suffice it to say that Prof. Zirkel divides the rocks for 

 purposes of classification according to their mineral constitution, 

 i. e., according to the feldspars or the lack of them, then accord- 

 ing to structure which goes band in hand with their geologic 

 position, that is, plutonic or effusive. For the effusive (or porphy- 

 ritic) rocks the distinction of geological age is retained, the rocks 

 thus being divided into paleo- and neo-volcanic. Rosenbusch's 

 family of the " dike rocks " is not recognized. 



"While it is probable that many petrographers will not agree 

 with Prof. Zirkel on various points of theory and classification all 

 will be thankful to him for the patient industry and rare discrim- 

 ination with which he has brought together and digested such a 

 vast amount of facts and material. These volumes when com- 

 pleted will form a work which no active investigator in this field 

 can afford to do without. It is to be hoped the work will event- 

 ually be thoroughly indexed. l. v. p. 



2. JJeber das Norian oder Ober-Laurentian von Canada, by 

 F. D. Adams. — Of this memoir, in which Dr. Adams sums up the 

 results of five years' work in the field supplemented by further 

 study with the microscope and in the laboratory, it may be justly 

 said that it is one of the most important contributions to the 

 proper understanding of the Archsean in Canada that has yet 

 been made. It is impossible to give here even a brief summary 

 of the results attained. He proves that the so-called " anortho- 

 site" rocks of Canada are of igneous character, that they have 

 broken through the Laurentian and are in general massive in struc- 



