228 NATURAL SCIENCE. Sept.. 



Chemical and Micro-Mineralogical Researches on the Upper Cretaceous 

 Zones of the South of England. By William Fraser Hume, D.Sc, etc. 

 8vo. Pp. 104. 3 Tables. London : [Printer — Whitehead, Morris & Co., 

 9 Fenchurch Street], 1893. 



This publication is, we believe (though it is not so stated), the 

 author's thesis for the degree of D.Sc. of London. It is the most 

 interesting contribution that has appeared for some time on the 

 Cretaceous rocks, and bears evidence of a vast amount of laborious 

 and painstaking research. Commencing with the Chalk Marl, the 

 author gives chemical and mineralogical analyses of the washings of 

 samples of 80 grammes average weight of each of the zones of the 

 Chalk, from the Chalk Marl to the Belemnitella mucronata zone, and 

 also discusses the micro-zoological remains which occurred in the 

 residues. The samples were mostly taken from the immediate neigh- 

 bourhood of some distinctive fossil, so as to be typically characteristic 

 of the zone to be examined. Each zone is treated separately and in 

 detail, the chemical analysis coming first, then the organisms, thirdly, 

 the secondary minerals, and, lastly, the detrital minerals. 



The author has wisely taken into his confidence specialists in 

 their Own departments, and has thus not fallen into the fatal error of 

 describing everything that came into his hands. Thus, Dr. Hinde 

 has looked over the sponge spicules, and Mr. Chapman has examined 

 the Foraminifera. Towards the end of the paper we find a summary 

 of results, and here Dr. Hume discusses the secondary silicification of 

 Foraminifera in a clear and exhaustive manner. He says, " there 

 seems little reason to doubt that considerable replacement of the 

 calcareous constituents by colloid silica has taken place," and he notes 

 that the most delicate interior divisions are in a fine state of preserva- 

 tion, after the residue has been treated with acid. So complete has 

 this replacement been in many cases that, in the process of solution 

 by acid, the bubbles issue from the mouth only of these microscopic 

 tests. Following these mineralogical notes, Dr. Hume mentions a 

 comparative identity between the foraminiferal fauna of the Chalk 

 Marl and the Gault, and commenting on the depths at which many 

 forms live in recent seas, inclines to the view that the Chalk Marl was 

 deposited at a depth of from 350-500 fathoms. No new light has 

 been thrown by Dr. Hume's researches upon the distribution of the 

 sponges in Cretaceous times, nor has he met with remains of Radio- 

 laria or Diatomaceae in the rock-specimens examined. 



In the general summary devoted to mineralogy, the author notes 

 the predominance of quartz in angular fragments, with occasional 

 crystals, worn and clear, in the lower Cenomanian beds. Inclusions 

 in quartz of apatite, rutile, tourmaline, ferruginous oxides, liquids, 

 and gases are recorded, and other forms of silica, as jasper and chal- 

 cedony, have been detected. Felspar occurs in Chalk Marl at Folke- 

 stone and in certain of the Turonian and Senonian beds of other 

 places, but it is much altered. Hornblende, augite, tourmaline 

 (widely distributed), zircon, rutile, garnet, glauconite, limonite, and 

 pyrite are also recorded in the paper. The glauconite abounds in 

 the Chalk Marl, but rapidly diminishes in the higher Cenomanian. 

 It reappears as an important constituent in the Chalk rock, and con- 

 tinues to form a considerable portion of the residue in all the lower 

 Senonian zones. Preference is given to the theory, in accordance 

 with Cayeux's views, that glauconite may be formed independently 

 of the presence of organisms. According to the author's observations, 

 the greater the thickness of the beds the more calcareous do they 



