Reviews — Gemstones in Museuin of Practical Geology. 89 



last-named deposit numerous sliells have been collected, and a list of 

 fifty-two species, revised by Mr. A. S. Kennard, is given. The last 

 chapter is devoted to economic geology, and deals with soils, road- 

 metals, and building materials; and the hydrology of the district is 

 briefly discussed. 



III. — Guide to the Collection of Gemstones in the Museum of 



Pkactical Geology. By W. F. P. McLintoce, B.Sc. pp. iv + 92, 



with 43 figures iti the text. Printed for His Majesty's Stationery 



Office. 1912. Price 9^. net. 



ri"^HIS Guide seems to have been overlong in passing through the 



jL press. The preface, which was written by the Director of the 



Geological Survey, is dated March 29, but more than eight months 



elapsed before the book actually appeared. 'No doubt the delay 



was partly caused by Mr. McLintock's transference to Edinburgh. 



His Majesty's Stationery Office, under whose auspices the book has 



been printed, cannot be congratulated upon the quality of the paper 



or the general get-up of the book. 



The Guide is intended to serve the twofold purpose of enabling the 

 visitor to find the various gemstones among the non-metallic minerals, 

 with which they are incoi'porated in the Museum collection, and to 

 identify cut specimens by certain physical characters. It is divided 

 into four chapters, which, on the whole, follow the usual lines : 

 (1) the pi'operties of gemstones, (2) the cutting of gemstones, (3) the 

 imitation, treatment, and artificial formation of gemstones represented 

 in the collection, (4) the description of gemstones. The author of 

 a guide of this kind is faced with the problem how to avoid technicality 

 which would repel the ordinary visitor, and yet to include enough 

 information to make it of real use. On the whole, Mr. McLintock 

 has steered a deft course, and has provided much interesting and 

 readable matter, which is purchasable for a very modest sum. 



The specific gravity is the character upon which most reliance is 

 placed for distinguishing one species from another, and various methods 

 for determining it are described. This test unfortunately necessitates 

 the stone being unmounted, and is not very convenient for the retail 

 jeweller or the purchaser of jewellery. The use of an ordinary 

 balance for the purpose might, with advantage, have been described, 

 since few jewellers possess the Westphal balance. The more generally 

 useful test depending on a measurement of the refractive indices and 

 the double refraction is only just alluded to, and the amount of 

 information given is too small to explain the method. In the 

 instrument mentioned on p. 16 the indices are read off directly on 

 a scale, and no calculations are needed as the reader might be led to 

 suppose. The dichroscope and its applicability are more fully dealt 

 with, and in an interesting paragraph the effect of radium emanations^ 

 upon the coloration of gemstones is discussed. The Museum collection 

 contains some fine specimens, including the gold snuffbox, set with 

 sixteen brilliant-cut diamonds and the large vase of avauturine 

 quartz which were presented to Sir Roderick I. Murchison by the 

 Czar Nicholas I, and the large vase of " Blue John", which is one of 

 the finest examples of this kind of work existing. 



