176 Reviews — Brief Notices. 



changes that render it softer ; but it is highly questionable whether 

 the sodium-salts which it contains ai'e derived froru the preservation 

 of original sea-water. The amount of sodium chloride has, however, 

 been found to decrease in certain localities where pumping lias been 

 in progress for some time, and Mr. Barrow suggests that a part of 

 the replaced calcium has passed into the form of a calcium-salt in the 

 interstitial matter of the rocks. 



Exceedingly important are his remarks on the relation of the 

 water-supply in the Chalk to the geological structure. Not only are 

 the effects of heavy loads of Eocene strata adverse to fissures and 

 fi'ee circulation of water in the Chalk, but it is important to consider 

 the undulations and faults in that formation. Thus the passage of water 

 through the Chalk, apart from fissui'es, is dependent on the water- 

 level, and is influenced by the litliological nature of the Chalk, and 

 still more by the pressure of the head of water towards the margins 

 of the basin. The consideration of these matters is greatly lielped 

 bj^ two colour-printed maps prepared by Mr. Wills. One shows 

 the contours in the underground water-surface or water-table of the 

 London District for 1911 ; and the other shows the contours in the 

 Pre-Tertiary Chalk surface, or, in other words, the height above or 

 depth below Ordnance Datum at which the Chalk occurs where overlain 

 by Eocene strata. Small maps are also inserted, for comparison, to 

 show the underground water-contours in the London Chalk in 1878, 

 between 1890 and 1900, and in 1911. Mr. Barrow is thus able to 

 discuss the areas of maximum and minimum water-supply, and the 

 causes for the distribution and local depletion. Moi'eover, the question 

 of the drawing in of impure water from the valley gravels, where 

 they directly overlie Thanet Sand and Chalk, and possibly of water 

 from the Thames in certain low-lying localities, is engaging serious 

 attention, as noted some few years ago by Mr. Clayton Beadle. 



The effects of pumping carried out towards the margin of the 

 London Basin are to decrease the head of water that would otherwise 

 press towards the centre of the basin ; moreover, the underground 

 circulation is affected by the light or heavy loaded Eocene areas, as 

 well as by the character of the Chalk itself. Mr. Barrow regards it 

 as urgently necessary to raise once more the water-level in the London 

 Basin, and suggests that much might be done by means of dumb- 

 wells on the outskirts of the London District. Needless to say, his 

 essay is one that will repay attentive study by all interested in the 

 subject of water-supply from the Chalk. 



V. — Brief Notices. 

 1. Union of South Africa : Mines Department. — We have 

 received the Annual Reports for 1911 of the Geological Survey of the 

 province of Transvaal (pt. iii, 1912, price 7s 6<^.). This volume 

 contains a useful map, scale 1 inch to 30 miles, showing the areas 

 surveyed up to the end of 1911. It may be mentioned that the 

 report of the Director, Mr. H. Kynaston, is printed in Dutch as well 

 as in English. The field-reports include one on " The Lower 

 Witwatersrand System on the Central Eand ", by Dr. E. T. Mellor, 



