28o PETROLOGICAL ABSTRACTS AND REVIEWS 



relatively small bodies. Syenite, diorite, quartz diorite, gabbro, peri- 

 dotite, and granite occur, the latter being rather uncommon. The rocks 

 are given the standard names, no attempt having been made to determine 

 them in the Cross, Iddings, Pirsson, Washington system. 



A. J. 



Jevons, H. Stanley, Jensen, H. I., Taylor, T. G., and StJss- 

 MiLCH, C. A. "The Geology and Petrography of the Prospect 

 Intrusion," Jour, and Proc. Roy. Soc. N.S. Wales, XLV (191 1), 



445-S53- 



About 18 miles from Sydney, in the midst of the VVianamatta 

 (Triassic) shales, occurs a massive intrusion of an augite-plagioclase rock. 

 The mass is roughly oval in shape, two miles long by one mile wide, and 

 forms a ring inclosing an isolated area of the shale. Numerous exposures 

 show this shale to be nowhere more than a few feet thick, and the igneous 

 rock is everywhere continuous beneath it. The main rock consists of 

 titaniferous augite 36 per cent, a zonal feldspar 36 per cent, olivine 10 

 per cent, ilmenite and magnetite 13 per cent, with biotite and apatite as 

 accessories, and analcite secondary. The plagioclase is called an acid 

 labradorite by the authors. Its central portion is labradorite (Ab3An4), 

 the rim is oligoclase (Abe Aui), and the average composition of the whole, 

 by analysis, Ab4An3. The authors believe the analcite to have been 

 derived from the feldspar, and not from a pre-existing nephelite. They 

 regard it as distinctly secondary. 



Surrounding the central mass of the intrusion is a shell of a very dark, 

 compact, gray rock, having the appearance of basalt. It not only forms 

 the outer zone, but occurs at the contact with the central mass of shale 

 as well, showing that it is actually a mantle around the entire mass. 

 This rock grades into that of the main mass, the size of grain gradually 

 increasing. 



The main mass of the Prospect rock has always been called a dolerite 

 in the sense of Teall, Hatch, et al., and not in the German sense, or a 

 diabase in the sense of Harker. The outer zone has been spoken of as 

 basalt or olivine basalt. On account of the association of the rock with 

 nephelite rocks, and the presence of as much as 18 per cent of orthoclase 

 and a little aegirite-augite in some of the segregation veins, the authors 

 regard the rock as a basic differentiation product of an alkali mother 

 magma, wherefore they give to it the name essexite. To the border they 

 give the name pallio-essexite, the prefex being applied by Mr. Jevons to 

 denote the compact envelope of any rapidly cooled igneous rock. In 



