Reviews — The Calvert Boring. 469 



III. — The Caltert Boeing. 



rpHE interesting and important record has now been published by 

 1 Dr. A, Morley Davies and Mr. John Pringle (Quart. Journ. 

 Geol. Soc, Ixix, p. 308, 1913) on the strata proved in two deep 

 borings at Calvert Station, on the Great Central Railway, in North 

 Buckinghamshire. It exemplifies the need, expressed by Dr. Strahan 

 in his Address to the Geological Society in February last, "that 

 registration of deep borings in a Government Department should be 

 made compulsory." Eeaders of the Daily Mail (October 18, 1911) 

 will have been struck with the announcement, printed in bold type, 

 of " Coal within SO^miles of London", and with the advertisement 

 of " The Bucks Coalfields Syndicate, Limited". It appears that the 

 notion that coal occurred was based on the fact that inflammable gas, 

 termed ' coal gas ', was encountered below depths of 380 and 443 feet. 

 This was " taken as an evidence of the possible existence at a shallow 

 depth of a deposit of bituminous coal" ; and in some newspapers the 

 statement was made that coal-seams had been struck at a depth of 

 530 feet. The presence also of "mottled red sandstone" was referred 

 to as " very promising for coal at a shallow depth ". The mottled 

 beds are now shown (in the paper above-mentioned) to be stained 

 Tremadoc shales (Cambrian, 443 to 1,398 feet) ; and they are overlain 

 directly by Lower Lias. It is suggested, however, that the staining 

 might be due to a former covering of Triassic strata. The Calvert 

 gas, which is stated to resemble that obtained from Wigan Cannel-coal, 

 occurred below the base of the Lias, and Dr. Davies and Mr. Pringle 

 mention as a possibility that the gas " may have leaked into porous 

 Triassic strata from underlying Coal Measures, possibly at some 

 distance to the west or north-west ". 



IV. — Diffusion" in relation to the Stetjctitee oe Agates, etc. 



Geologische Difeusionen. By R. E. Liesegang. pp. viii + 180, 

 with 44 figures in the text. Dresden and Leipzig : Theodor 

 Steinkopff, 1913. 



r^ EOLOGISTS interested in the structure of agates, concretionary 

 Vjr nodules, and similar objects, should not fail to read Dr. Liesegang' s 

 extremely fascinating book. Recent chemical work on diffusion has 

 thrown quite a novel light upon the possible cause of the markings 

 characteristic of such structures, but may not be generally known to 

 geologists, because some of the journals in which many of the original 

 papers appeared do not usually circulate among them. The author 

 has therefore done excellent service by bringing together the somewhat 

 scattered literature on the subject, and showing how closely the results 

 obtained in the laboratory parallel the phenomena actually met with' 

 in nature. A valuable and important feature of the book consists of 

 the extensive series of experiments on diffusion which is interwoven 

 in the text to illustrate the particular points dealt with. The salts 

 and materials used in them are all easily procurable, and the careful 

 explanations render it easy to repeat any of the experiments. 



The scope of the book is comprehensive in character. It opens 



