174 SCIENCE PROGRESS 



carried somewhat too far. It is only right that every rock-name which has been 

 employed by a writer of authority should be explained, but only a selection need 

 be recommended for adoption by the student. 



In a few cases the author has given a new connotation to well-known terms. 

 For instance, he uses the expressions nepheline basalt and lencite basalt for rocks 

 containing those minerals but no felspar, and does not make the presence of 

 olivine a necessary part of the definition as required by present usage, according 

 to which such rocks when free from olivine are known as iiephelinite and leucitite. 

 The present method of employing these different names is illogical, but it is accepted 

 and understood by petrologists of all nationalities, and it seems a pity to introduce 

 a new ambiguity into a department of science where so many already exist. A 

 better mode of simplifying the nomenclature, which would not be open to the same 

 objection, would be to call rocks containing the felspathoid and olivine, but no 

 felspars, olivine nephelinite or olivine leucitite, as the case might be. 



Dr. Hatch adopts a suggestion of Lindgren and accepts the principles of the 

 American classification to the extent of calling a rock a syenite if the alkali 

 felspar bears to the soda-lime felspar a ratio of more than two to one ; a monzonite 

 if less than two to one and more than one to two, and a diorite if less than one to 

 two. The irregular distribution of minerals in igneous rocks would make these 

 distinctions very unsatisfactory and inconvenient. 



The author concludes with abstracts of most of the classical descriptions of 

 igneous rocks in the United Kingdom, accompanied by reproductions of the 

 original maps by which they were illustrated. This portion of the work should 

 prove of special value to the student. The representations of rock slides, many 

 of which are supplied by Mr. Rastall, are very effective. Some of the older 

 figures that still remain will no doubt be replaced in another edition. This should 

 certainly be the case with the drawing on p. 105 of a hornblende crystal repre- 

 senting an interpretation now everywhere abandoned. 



The table for the determination of the chief minerals of the igneous rocks, 

 -which forms an appendix, will be appreciated by the elementary student. Arf- 

 vedsonite and riebeckite should not, however, have been included among minerals 

 with " strong double refraction." 



The use of the index, which is due to Mr. Pringle, is facilitated by the adoption 

 of different type for place-names, rocks, and other matters. 



J. W. Evans. 



The Commercial Products of India, being an Abridgment of the 

 " Dictionary of the Economic Products of India." By Sir George 

 Watt, CLE., M.B., LL.D., etc. Published under the authority of his 

 Majesty's Secretary of State for India in Council. [Pp. viii -f 1189.] 

 (London : John Murray, 1908. Price 16s. net.) 



The standard work of reference on the economic products of India has been, for 

 many years, the Dictionary referred to in the sub-title with its continuation the 

 Agricultural Ledger. Both were produced by the Reporter on Economic Products 

 to the Government of India, an appointment held until quite recently by Sir 

 George Watt. 



The Dictionary, in eight large volumes, published between 1885 and 1894, has 

 for some time been out of print. Moreover, during the period of close upon 

 a quarter of a century which has elapsed since the first volume appeared, a 

 considerable amount of knowledge has been accumulated regarding Indian 



