22 Revieius — The Coal Resources of the World. 



The opinion is expressed tliat the best explimation of these 

 phenomena has been given by Pechuel-Lcisclie, who ascribes them 

 to the sudden cooling produced by a torrential rain falling upon 

 highly heated surfaces. Attention is called to the intensity of physical 

 change when rain at 20° C. or hail at 0° C. suddenly falls on rocks 

 heated to 80° C. ^Numerous small cracks are produced due to cooling, 

 subsequently often enlarged by temperature variations in blocks 

 suitably exposed. 



He also mentions the extraordinary cavernous weathering ex- 

 hibited by rocks of heterogeneous composition and variety of minei-al 

 colouring, such as the granite (see fig. 73). The variously coloured 

 constituents expand with varying rapidity under the solar influence, 

 and also in cooling contract at different speeds. This constant inter- 

 play causes a loosening of the individual particles, so that it is very 

 difficult to obtain a solid specimen of typical red granite or other 

 igneous rock in the Red Sea Hills or Sinai. To this breakdown he 

 ascribes the frequency of sand-slopes among the granitic hills, the 

 wind sorting out the materials, the quartz remaining to form the 

 dunes, while the mica is swept onward into protected places and 

 the felspar rapidly breaks up into cleavage fragments. 



{To be concluded in our next Number.) 



:k,e"vi:e]'';7\7"S. 



I. — The Coal Eesoukces of the "Woeld : an enquiry made upon 

 the initiative of the Executive Committee of the Twelfth 

 ' International Geological Congress, Canada, 1913, with the 

 assistance of Geological Surveys and mining geologists of different 

 countries. Edited by "William McInnes, E.A., E.R.S.C., D. E. 

 DowLiNG, B.A. Sc, F.E.S.C, and W. W. Leach, B.A. Sc, 

 of the Geological Survey of Canada. 3 vols. Crown 4to ; 

 pp. 1266 -f- civ, with plates and illustrations in the text and 

 accompanied by an atlas of maps. Toronto, Morang & Co. ; 

 London, Dulau & Co. ; 1913. Price £5 5,9. 



IT is a truism that a deposit of iron-ore is of no value if there is no 

 supply of coal. This comprehensive and valuable work, chiefly 

 written in English, therefore forms a fitting sequel to the monograph 

 on the iron-ore resources of the world issued by the Eleventh 

 International Congress in 1910. The present volumes, in a series of 

 articles written by experienced geologists and mining engineers, 

 afford valuable information about all the known coal-bearin"- 

 regions of the world. In the case only of Greenland, Peru, and 

 Brazil has it been necessary to compile from published literature, 

 so that the monograph affords the latest and most authoritative 

 pronouncement on the "coal resources of the world" and replaces 

 all previous literature on the subject. 



To review adequately such a large amount of information is here 

 impossible ; a brief resume of the general scope of the work, with 



