3Q 



University of California. 



[Vol. i. 



various facies. The fresh rocks exposed in the sea cliffs are usually 

 of a dark bluish gray color, while the sub-aerially weathered portions 

 are of a yellowish or pinkish color, or have a bleached appearance. 

 Sometimes they are rusty or ocherous on the surface. Some varie- 

 ties have a yellowish or greenish gray color on the freshly broken 

 surface. 



The variation is, moreover, not confined to the macroscopic 

 features of the rock. When viewed in thin section on the stage of 

 the microscope, or when investigated chemically, it is far from uni- 

 form in character. Glass is abundant in some sections, while others 

 are more nearly holocrystalline. Among the porphyritic constituents 

 augite and plagioclase vary much in the proportion in which they 

 are present. In most facies one or both of these minerals may be 

 lacking among the phenocrysts. Chemical analysis has shown that 

 the silica content has a range of at least from 52 per cent, to 60 per 

 cent., the former figure being usually regarded as too low for the 

 andesites and the latter as too high for the basalts. There is thus 

 some trouble in properly classifying them in the current petrograph- 

 ical schemes. In consideration of this fact and of their very pecul- 

 iar mineralogical character, these rocks will be referred to in this 

 paper under the name carmelaite, their strong individuality being 

 ample warrant for the new name. 



The common characteristic of all facies of these eruptive rocks 

 is the presence, as a phenocryst of a mineral which, by reason of 

 its rarity and the obstacles to investigation which it presents, has 

 received but little attention at the hands of petrographers and miner- 

 alogists. So scant are the references to it in mineralogical literature 

 that, notwithstanding its distinct specific character, it has not yet 

 been signalized by a name. The most extended and satisfactory 

 note that has yet appeared regarding it is by Prof. J. P. Iddings,* in 

 a work which has recently been published and which reached the 

 writer after this investigation on the mineral in question had been 

 completed. For this reason and also in recognition of Professor 

 Iddings' eminent services to the science of petrography, it is proposed 

 to name the mineral iddingsite. 



*Geology of the Eureka District, Nevada. Monograph XX U. S. G. S., 

 Appendix B, pp. 3S8-390. 



