560 CROSS, IDDINGS, P IRS SON, WASHINGTON 



PART I. CLASSIFICATION. 

 INTRODUCTION. 



The commonly acknowledged unsatisfactory character of rock 

 classifications in present use, and the unsystematic nomenclature 

 of petrography, have convinced us of the necessity for a com- 

 plete reconstruction of both. Recognizing the magnitude of this 

 task, yet desiring to see it accomplished as early as possible, we 

 have united our efforts toward the production of a new system 

 of classification and the creation of a nomenclature to express it. 

 Many attempts at improvement of existing schemes of classifi- 

 cation have been made in recent years, but they have failed to 

 accomplish important results because they have not gone to the 

 root of the matter. 



The discussions of petrographers associated with the Inter- 

 national Geological Congress have demonstrated the futility of 

 attempting the regulation of petrographical nomenclature with- 

 out first fixing the basis of rock classification, since the concep- 

 tions by different petrographers of the objects to be named are 

 diverse. And the effort to establish a systematic classification 

 of igneous rocks by international conference and agreement has 

 in like manner proved ineffective because of evident inherent 

 difficulties. 



The recently published Compte Rendu of the Eighth Session of 

 the International Geological Congress, held in Paris, furnishes an 

 illustration of the diversity of views held by European petrogra- 

 phers, while presenting in definite form the convictions of a consid- 

 erable number of the foremost workers in this science regarding 

 the principles that should govern the choice of bases of a sys- 

 tematic classification. To a very considerable extent we find our- 

 selves in accord with the opinions expressed in the report of the 

 Russian Committee and in the discussions and report of the Paris 

 Commission of October, 1899. And we are encouraged to hope 

 that the system here presented by us will meet with a cordial 

 reception by those petrographers who, sharing more or less 

 completely our conceptions of the fundamental principles that 



