176 Reviews — Dr. F. H. Hatches Text-Book of Petrology. 



evidence. The results are interesting, and the experiment is well 

 worth repeating ; it suggests a resemblance to the occurrence of 

 diamonds in epidiorite in Australia. 



The groundwork of the geology of the country is a complex of 

 gneisses, amphibolites, and schists of many different kinds, hut 

 apparently all igneous. This has been reduced by erosion to a 

 peneplain and covered by extensive deposits of sandstone, relics of 

 which now form flat-topped mountains. Some of these, like Mount 

 Koraima, have a considerable elevation. The sandstones are probably 

 Cretaceous, though in British Guiana they have not yielded any fossils. 

 The various Palseozoic rocks which are known in the Amazon Yalley 

 apparently do not occur in British Guiana. At the base of the sand- 

 stones there are dykes and sills of diabase which Mr. Harrison suggests 

 may belong to the Tertiary Cordilleran or Pacific magmas, but opinions 

 differ as to the relations of these rocks, and there may be two diabases, 

 one older and one newer than the sandstones. The petrographical 

 characters of the fundamental complex are very fully described. They 

 have many affinities to the Lewisian rocks of JSTorth-West Scotland. 

 The quartz diabases are excellent representatives of a type which has 

 been repeated with identical characters at many different epochs over 

 the whole world. Many analyses of the metamorphic and igneous 

 rocks are given, and the excellence of Mr. Harrison's analyses is known 

 to all petrologists. Some photomicrographs appear, unfortunately not 

 accompanied by any descriptions. The volume also would be improved 

 by the insertion of a map, if only as a guide to the topographical 

 details. In spite of minor defects the work deserves high praise ; it 

 shows how much can be done, even in a country Avhere the physical 

 difficulties are extremely great, by the continued researches of a resident 

 geologist. Even the most accomplished visitor can do little in such 

 a region. jS'o part of the British West Indies is so well described as 

 British Guiana, and in the whole of South America there are only 

 a few small portions so well known in a geological sense. We have 

 reason to be thankful for the intelligent policy of the colonial adminis- 

 tration which has made it possible for scientific work of this character 

 to be carried to completion. 



J. s. r. 



II.— Text-Book of Petrology. By F. H. Hatch, Ph.D. Fifth 

 Edition. pp. xvi -|- 404, with 130 figures. London: Swan, 

 Sonnenschein, & Co., Ltd. New Tork : The Macmillan Co. 

 1909. Price 7s. &d. net. 



IT is eighteen years since Dr. Hatch issued a slim volume entitled 

 Introduction to the Study of Petroloyy. So immediate was its 

 success, and so great the demand for it, that only two years later 

 a second edition appeared under the more extensive title which has 

 been retained in the subsequent editions. Although two editions 

 have been issued during the intervening years, they are merely reprints 

 of the second, and there has, therefore, been really no fresh edition 

 since the second. These years have marked a period of great activity 

 in petrological science. Important improvements have been introduced 

 into the petrological microscope, and more subtle methods have been 



