Reviews — Volcanic Rocks of the Ross Archipelago. 281 



and border deposits, (2) internal segregations, (3) fissure and fault 

 veins from deep-seated sources: furthermore, a definite primary 

 zoning exists in the fissure-veins, and the horizon of ore- 

 precipitation migrates regularly downwards in the successive stages 

 of mineralization. All the facts here put forward are clearly 

 consistent with the view that the mineralizing solutions are direct 

 products of magmatic differentiation, when allowance is made for 

 modifications introduced by the ordinary processes of chemical 

 change and secondary enrichment that go on to a greater or less 

 extent in all mineralized areas. This admirable study may be 

 strongly recommended to the attention of all geologists interested 

 not only in ore-deposits, but also in the theoretical side of 

 pedogenesis. 



R. H. R. 



IX. R,Er01tT ON THE INCLUSIONS OP THE YoLCANIC RoCKS OF THE 



Ross Akchipelago. By J. Allan Thomson. British Antarctic 

 Expedition, Geology, vol. ii, pp. 131-51, with 3 plates and 

 3 text-figures. London, n.d. 



NUMEROUS specimens of nodules and inclusions in the igneous 

 rocks were examined by the author, who concludes that the olivine, 

 pyroxene, and gabbroid nodulesin the basalts and limburgites of Hut 

 Point were formed by normal differentiation from the magma itself . 

 In the trachytes and kenytes are found nodules of sanidine and 

 plagioclase : it is not quite clear whether these are magmatic 

 segregations or included xenoliths. Hornblendic inclusions in the 

 trachytes, such as those at Observation Hill, are believed to be 

 inclusions, but those at Cape Bird seem to be xenoliths of camptonite. 

 The plagioclase-pyroxene inclusions in the trachyte of Mount Cis 

 appear to be metamorphosed fragments of dolerite, possibly torn off 

 from sills in the Beacon Sandstone. The quartz-bearing masses in the 

 trachytes and kenytes are certainly altered fragments of impure sand- 

 stone : they contain a lot of glass and are very vesicular. There are, 

 therefore, two distinct categories: (1) segregations, (2) xenoliths. 

 It follows that parts of the Ross Sea are underlain by sandstones, 

 probably faulted-down Beacon Sandstone and the presence of the 

 lumps of dolerite confirm this idea, since in this formation dolerite 

 sills are abundant and characteristic. 



X. — Kongsbebgfeltets Geologi. By C.~ Bugge. Norges. Geol. 

 Undersok, No. 82, with English Summary, pp. 272, with 

 12 plates. Kristiania, 1917. 



ALL the rocks of the famous Kongsberg mining district are of 

 pre-Cambrian age, except certain diabase dykes, which are 

 supposed to be post-Silurian. The older Knute formation consists 

 mainly of volcanic rocks converted into amphibolites and gneisses, 

 with some schistose sediments. Into these are intruded laccoliths of 

 granite, quartz-mica-diorite, and gabbro-diorite, as well as hypabyssal 

 representatives of these magmas ; petrographical descriptions are 

 given of these rocks and the properties of their constituent minerals 

 are described. 



