478 REVIEWS 



they might be younger than pre-Cambrian. The youngest rock is a 

 diabase, which occurs as intrusive sheets and flows. The evidence for 

 and against the diabase occurring as a volcanic flow is fully discussed, 

 the conclusion being that as now known they are basal residuals of 

 former extensive flows. 



The glacial geology is briefly discussed, the author concluding that 

 ice erosion was very limited, except locally. The physiographic features 

 are considered, also the economic geology, but no deposits ot any value 

 are known. 



W. A. T. 



The Geology and Ore Deposits of the West Pilbara Gold field. By 

 H. P. Woodward. Bull. No. 41, Western Australia Geologi- 

 cal Survey. Pp. 142; 5 geological maps; 1 mining plan; 

 25 figs. 



The first part of the bulletin is devoted to a general discussion of 

 the physiography, geology, and petrography of the district, which 

 occupies the triangular portion of the northwest division of the state 

 included between the Fortescue and Yule rivers. The southern part 

 of the area is a high tableland which drops abruptly to the wide, low 

 coastal plain forming the northern part. 



The oldest rocks in the region are metamorphosed sedimentaries — 

 clay slates and shales — that have been intruded successively by dolerite, 

 gabbro, and granite. The last is thought to have altered some of 

 the clay slates and dolerites to crystalline schists. A period of sub- 

 sidence was accompanied by an outburst of volcanic activity in the form 

 of fissure eruptions of very fluid basic lava. Subsidence continued, and 

 marine beds are found above the last lava flow. Re-elevation and 

 denudation have given rise to the present topography. The various 

 formations are described in some detail, and petrological notes on 

 seventy specimens are appended. 



The second part of the bulletin is devoted to a more detailed descrip- 

 tion of the country and the mining centers visited. The lodes are most 

 frequently found in the altered sedimentaries. They carry, in addition 

 to gold, varying amounts of pyrite, chalcopyrite, and galena. Little 

 evidence regarding the genesis of the lodes is presented. Much of the 

 material is of greater interest to the engineer and the investor than 

 to the geologist. 



A. D. B. 



