426 PROCEEDINGS OF THE ACADEMY OF [Aug... 



AN ARRANGEMENT OF MINERALS ACCORDING TO THEIR OCCURRENCE.^ 

 BY EDGAR T. WHERRY AND SAMUEL G. GORDON. 



In the preparation of a catalog of the minerals of Pennsylvania, 

 upon which the writers have been engaged for some time, a system- 

 atic plan for listing the minerals under each locality has proved 

 desirable. The standard classification, as used by Dana, being unsatis- 

 factory for this purpose, in that it is based on chemico-crystallographic 

 features, and represents a laboratory rather than a field system, 

 a new arrangement, based on occurrence and genetic relationships, 

 has been worked out. 



The principles applied require little discussion. The types of 

 mineral occurrence are classified on the basis of chemical and geo- 

 logical relations, the chief criterion for subdivision being dissimilarity 

 in mineral content. Thus, granite is not separated from syenite, 

 since both are made up of essentially the same minerals; but low- 

 alkali syenites are separated from those high in alkalies because 

 quite different minerals develop in the two. The various sub- 

 divisions are not sharply defined, but grade ijnto one another, so 

 that rather arbitrary lines must be drawn between them; for example, 

 certain types of veins, such as the tourmaliniferous copper veins, 

 might with equal right be classed with either pneumatolytic veins 

 or hydrothermal deposits, and their minerals are here arbitrarily 

 placed in the former class. However, every effort has been made 

 to minimize difficulties of this sort by making the subdivisions as 

 comprehensive as possible. In arranging the minerals in each 

 division, Dana's order has been more or less closely followed. 



Rather than coin new names for the several subdivisions of this 

 scheme of classification, we have employed terms in common use, 

 even though they are not altogether appropriate. Thus "hydro- 

 thermal" is used for mineral veins, as is customary with economic 

 geologists, although it is recognized that pegmatites and, for that 

 matter, even ig-neous rocks, have about as much right to this term, 

 since both water and heat contribute to their formation. The terms 

 silicic, alkalic, calcic, and magnesic for the chemical subdivisions are 

 intended to indicate only the prominence of the respective con- 



' Presented at the meeting of the Mineralogical and Geological Section of the 

 Academy, December 14, 1914. 



