Reviews — The Geology of tJie Plateau Tin Fields. 477 



j)ilations, in that the sources of available information are of unequal 

 value and reliability. To take a concrete example, it must be frankly 

 said that the account of the iron ore resources of the British Isles 

 is inadequate and misleading : unfortunately the recent admirable 

 publications of H.M. Geological Survey on this subject are not 

 mentioned and have evidently not been consulted, and the map of the 

 Cleveland district is entirely unintelligible to the reviewer, although 

 it is said to be reproduced from " The Iron-Ore Resources of the 

 World " (International Geological Congress, 1910). Good summaries 

 are given of the minette ores of Lorraine, of the Spanish deposits, 

 and of the verv interesting magnetite and other ores of Sweden. 



The author has ransacked very fully the available literature on 

 the less-known localities, and has compiled an extremely useful 

 bibliography, arranged by countries. 



The Geology of the Plateau Tix Fields. By J. D. Falconer. 

 Bulletin I, Geological Survey of Nigeria, pp. 55, with 10 plates 

 and a coloured geological map. Published by the Nigerian 

 Government, 1921. Price 10s. net. 

 rPHE Geological Survey of Nigeria was established in 1919, under 

 -*~ the direction of Dr. J. D. Falconer : it has lost no time in 

 giving tangible jiroofs of its activities in the form of this and other 

 memoirs that have recently come to hand. The economic importance 

 of the tin deposits of Northern Nigeria is well known and the geology 

 presents some points of interest. The area here described consists 

 of a fundamental complex of ancient schists and gneissose granites, 

 the last named apparently of more than one age. At a later, but 

 unknown date, this complex was invaded by a great granite batholith 

 with a very irregular upper surface, now forming seven main out- 

 crops or groups of outcrops : with this intrusion are associated 

 numerous dykes and an extensive and well-marked mineralization 

 of the cassiterite-wolfram-topaz type, tourmaline being rare. The 

 Plateau granite carries mamly biotite, but locally there are highly 

 alkaline facies with riebeckite. Some of these types have been 

 described in more detail by Major Williams, to whose paper in the 

 Geological Magazine no reference appears to be made : through- 

 out this.memoir very few references are given to previous literature. 



As in most tin-mining districts, nearly all the production has 

 hitherto come from alluvials, but in many localities there are 

 promising indications of the presence of stanniferous veins and lodes, 

 though none yet appear to have been worked with success. It is 

 possible that much of the most highly mineralized granite has 

 already been removed by denudation and distributed into ancient 

 or modern alluvial deposits. 



A considerable part of the district here described is covered by 

 what is called the Flu vio- Volcanic Series, consisting of much -decom- 

 posed lavas and redistributed volcanic material, partly burying, as 



