PROBLEMS OF PETROGRAPHIC CLASSIFICATION 8oi 

 CLASSIFICATION OF KODURITE SERIES BY HATCH's SYSTEM 



While Fermor considers the Quantitative Classification of the 

 Kodurite Series unsatisfactory, as illustrated by the four hypo- 

 thetical rocks specially discussed, he states that he is able to 

 classify the whole series with ease and accuracy in the modified 

 form of the mineralogical system recently proposed by F. H. Hatch/ 

 and draws the attention of the American petrographers to the 

 "elasticity of Hatch's classification."^ Believing the kodurite 

 rocks plutonic, Fermor adds "a mangan-subseries of the potash 

 series" and introduces the Kodurite Series intact, with its new 

 names, in Hatch's system. Whether Hatch considers this claim 

 for the elasticity of his system correct or not I do not know, but I 

 do not understand that any existing system permits the intro- 

 duction of local or provincial series as such in its framework. 



The discussion of Termor's procedure in applying Hatch's 

 system to the Kodurite Series may well be left to the author of that 

 system, but, as one who has studied the subject of systematic 

 classification of rocks from many standpoints, I wish to make the 

 comment that the principles of general system and the consider- 

 ations that control in the expression of provincial characteristics in 

 a so-called "rock series" are almost antithetical. A scheme con- 

 taining three or four such series intact would cease to be a system. 

 The term "series" is applied by Hatch and termor to very differ- 

 ent concepts. 



It would seem to me that the case of the Kodurite Series was 

 directly covered by the following statement of Hatch: 



Although names founded on mineralogical variation in constituents other 

 than the feldspars are of little service in classifying rock-types, they are often 

 useful for descriptive purposes. They form no part, however, of the system 

 of classification now undergoing discussion .^ 



hatch's PETROGRAPHIC SYSTEM 



The classification of igneous rocks presented by Hatch in the 

 fifth edition of his Textbook of Petrology (1909), and repeated in 



^ F. H. Hatch, "The Classification of the Plutonic Rocks," Science Progress, 

 October, 1908; Textbook of Petrology, 5th ed., 1909; 6th ed., 1910; 7th ed., 1914. 



^ Records, p. 225. ^ Science Progress, p. 7. 



