512 H. S. JEVONS, H. I. JENSEN, T. G. TAYLOR AND C. A. SUSSMILCH. 



That this course would not be opposed to existing practice 

 is, we think, clear from the close correspondence of the 

 Prospect rock, both in mineral and chemical composition 

 with the intrusive rocks of Solvsberg and Brandberg in the 

 Ohristiania region. These were named by Brogger olivine- 

 diabases, 1 but were soon after associated with the essexites 

 by Rosenbusch, 2 and this name for them has since been 

 very generally accepted. We prefer, therefore, to call the 

 main mass of the Prospect rock essexlte, and its compact 

 envelope, as already explained, pallio-essexite; but at the 

 same time there is no doubt that it is in accordance with 

 the usage of many authors at the present time to call the 

 main mass an olivine-dolerite, or diabase, and its envelope 

 an olivine basalt. 



The nomenclature of the Prospect rock, according to the 

 quantitative system of Cross, Iddings, Pirsson and Wash- 

 ington, has been found by ascertaining the norms of those 

 specimens which have been analysed. The calculated 

 norms are displayed in the following table, and they place 

 each of the rocks in the subrang camptonose. Specimen 

 L a fine-grained pallio-essexite from Emu Quarry (No. I) 

 and the specimen, probably from the Emu Quarry, which 

 furnished the analysis previously published, fall near 

 auvergnose (No. II), and should properly be called auverg- 

 nose-camptonose. The pallio-essexite (No. Ill of the 

 subjoined table), however, falls well within the boundaries 

 of camptonose. The mode and texture of the rocks.may be 

 indicated according to the rules laid down by the authors. 

 The main mass is a grano-augite-campbonose, and the 

 compact outer envelope is a pitaxi-biaugi-camptonose y 

 using the contraction pitaxi- to signify pilotaxitic. 



1 Quart. Journ. Geol. Soc, Lond. (1894) p. 18. 

 2 Mikr. Phys. II, (1896) p. 250. 



