Reviews — Brief Notices. . 91 



He then deals with tiie condition of the buried rocks, owing to the 

 preserving influence of tlie marl covering, and an interesting chapter 

 is devoted to the breccias, stone bands, and rock fragments contained 

 in the marls. On account of the uncertainty that existed as to the 

 mineral composition of the Keuper Marls, Mr. Bosworth made various 

 experiments, the result of which are given in some detail •, and in the 

 discussion of the mineral grains, an interesting comparison is made 

 between the larger grains of the heavj- minerals, now rounded and 

 smoothed, and those of a Scottish Carboniferous Sandstone, which are 

 in strong contrast. 



The author has for some years been collecting data as to the ripple- 

 marks, and he includes a table of observations in this direction. 

 These lipples were formed under shallow water, and were controlled 

 by the prevalent south-west wind. 



The last chapter summarizes the facts very clearly, and some 

 conclusions are drawn as to the mode of deposition of the sediments. 

 Mr. Bosworth offers as his interpretation that the sediments accumu- 

 lated in an inland basin that was partly dry and partly occupied by 

 comparatively deep standing pools, the climate being arid, and 

 evaporation in excess of precipitation. Streams of fresh water 

 flowed into the desert from the hills south-west, on which was 

 precipitated the moisture of the prevalent wind. At times most of 

 the desert would be dry, and the inflowing water would be spread 

 over the plains and be evaporated before reaching the pools. Tinder 

 these conditions the grey beds would be deposited, while the red 

 mai'ls accumulated in the standing pools. 



There are four short appendices to this volume, and these give 

 details of the sections at Gipsy Lane, Hathen, Sileby, and Whitwick. 



V. — Bkief N'otices. 



1. Oee-deposit, Dolores Mine, Mexico. — In Economic Geology for 

 August, 1912, Messrs. J. E. Spurr, G. H. Garrey, and Clarence ]S\ 

 Tenner give an interesting study of the metamorphic ore-deposit at 

 the Dolores Mine, situated at the east base of a small mountain range 

 near Matehuala, S.L.P., Mexico. The range, which is of blue 

 Mesozoic limestone, overlain by the shales forming the valleys on 

 both sides, is remarkable for an enormous fault of a vertical displace- 

 ment of 1,500 metres. There are two areas of intrusive quartz- 

 raonzonite, showing evidence of dawning magmatic differentiation 

 in situ, and near them are lime-silicate' rocks, the product _ of 

 metamorphism. The ore-deposition is in the order— copper pyrites 

 and pyrites, mispickel, pyrrhotite and pyrites, blende, galena, the 

 third stage being rich in sUver. Mr. Spurr elaborates his theory of 

 ore-deposition, one of the most important features of which is that 

 the metalliferous solutions from which ores are deposited originate in 

 and spring from the zone of igneous rock differentiation, which is in 

 the lower part of the zone of crystallization. 



2. In the American Joxirnal for Science for October, 1912, Mr. E. T. 

 Allen and Mr. J. L. Crenshaw discuss the various kinds of sulphides 

 of zinc, cadmium, and mercury, and the conditions under which they 



