134 PROCEEDINGS OF THE CORDILLERAN SECTION 



and act as dams to prevent tbe flow of water from the east to the west, as now 

 iin<lprstood. 



There are more than 400 artesian wells in the area of tlie Plioeene sediments. 



Paper presented witlioiit notes. 



Discussion 



In I'eply to question by Doctor Merriam, author discussed the number of 

 species represented in tlie supposed Plioeene, and claimed that only one was 

 definitely known to be extinct. Answering questions by Louderback, he said 

 that no deeper strata of possibly earlier age are known, and that no fauna 

 similar to the Ostrca retusa existed on the islands at the present time. 



Professor Lawson pointed out that the water found behind the dikes might 

 not be diverted flows, but natural reservoirs in which water was standing at 

 the time it was tapped, and compared some mine waters found behind gouge. 



PLEA FOR UNIFORMITY AND SIMPLICITY IN PETROLOOIC NOMENCLATURE 



BY G. MONTAGUE BUTLER 



(Abstract) 



In the nomenclature of no other science is there probably so much confusion 

 and uncertainty as in petrology and petrography. This is especially true as 

 regards the macroscopic classification of igneous rocks. 



A practical system is a necessity to mining engineers and field geologists, and 

 uniformity of nomenclature is undoubtedly highly desirable. The Geological 

 Society of America can well consider and decide this matter, as it has done in 

 the case of fault nomenclature. 



The classification adopted should fulfill the following conditions : 



1. The terms used should be old, well known ones so far as possible, and 

 the meanings assigned to them should correspond with common usage where . 

 this is practicable. 



2. The distinctions should be based only on features readily recognizable in 

 the field. 



H. The meanings attached to the various names should not be so compre- 

 hensive as to vitiate the usefulness of such names. 



4. The classification should be of such a nature that it may be readily ex- 

 tended, so as to include rocks whose identification depends on microscopic 

 iin estigation. 



Such a classification is offered. In it the igneous rocks are divided accord- 

 ing to textural distinctions, which result from solidification under different 

 conditions into three series, and the criteria of each series are given. 



The identification of individual rock species is then based on the recognition 

 of constituent minerals, and in the case of aphanitic rocks on color luster and 

 other features. 



In conclusion, the practical value of the conception of rock types is pre- 

 sented and the placing of emphasis on such types is defended, although it is 

 admitted that precautions must be taken to prevent the growtli of misconcep- 

 tiims in the minds of students when this practice is followed. 



Eead from manuscript. 



