

W. Cross — Igneous Rocks in Wyoming. 137 



even told by Rosenbusch that peridotite and pyroxenite are 

 annexes of the gabbros.* 



The fact that the names leucitite and nephelinite are cur- 

 rently applied to rocks in which leucite and nepheline are not 

 necessarily of much quantitative importance, also illustrates very 

 well the inadequate and illogical character of our present 

 petrographical nomenclature. The natural application of these 

 terms would be to rocks so rich in leucite or nepheline as to 

 derive their dominant mineralogical features from the charac- 

 teristics of these species. But as a fact one must search very 

 carefully with a microscope to detect any leucite in some of the 

 so-called leucitites. 



The leucite rock described by Zirkel, to which it is here 

 proposed to give the name wyomi?igite, has been placed in the 

 group of the leucitites by both Zirkel and Rosenbusch in their 

 latest systematic works, but with comments upon its exceptional 

 character, removing it far from its nearest ally in the group. 

 The new name is proposed for this rock in recognition of its 

 peculiar character, and also as a part of a scheme for reclassify- 

 ing the leucite rocks which it is hoped may find favor with 

 those who have to deal with this interesting class of igneous 

 rocks. 



As a first step, in spite of established usage, I should be glad 

 to see the term leucitite reserved for the rock that has not yet 

 been discovered, to my knowledge, consisting essentially of 

 leucite, with all other minerals of subordinate importance. 

 There is good reason to believe that such rocks are possible and 

 will be found at no distant day. The same suggestion is made 

 for nephelinite, on the same grounds. 



Following leucite would come the rock here called wyo- 

 mingite, and its granular equivalent, in which leucite and its 

 allies are of approximately equal importance with the ferro- 

 magnesian-lime silicates, and then a rock of which madupite is 

 deemed a vitrophyric representative. Leucite-sanidine, leucite- 

 nepheline and leucite-plagioclase rocks are known, or will be 

 found, in which these elements preponderate, and they are cer- 

 tainly very different from the types from which the present 

 nomenclature of leucite rocks has been mainly derived, where 

 leucite is of secondary importance. 



Reviewing the chemical and mineralogical characteristics 

 of the rocks under discussion, it is evident that they are notable 

 for their high contents in the alkalis, and especially for the 

 strong preponderance of potash over soda ; and although 

 wyomingite is one of the richest known rocks in leucite, it is 

 not this fact alone which gives character to it. Prominence 

 must be given to the fact, which is also true of the sanidine- 

 bearing orendite and of the madupite with its glassy base, that 

 * Massige G-esteine, 3d ed., pp. 344, 367. 



