424 Reviews and Book Notices. 



the last joint somewhat clubbed, as in figure a. JMany of the 

 hairs on the legs and palpi are beautifully feathered (see figure 

 /). The fourth joint of the palpus terminates in two claws 

 (figure /). The papillse on the dorsum are not crowded, and 

 in structure are very peculiar, reminding one of a savage war- 

 club. They are enlarged towards the distal extremity, and look 

 as if studded with spikes (see figures c, d and e). Even when 

 mounted in balsam they retain much of their colour, which 

 adds greatly to their beauty. I am sorry to say that I have 

 only seen one specimen of this mite, which deser\es more 

 detailed description. I think, however, that the peculiar 

 papillae are sufficient to differentiate it from other members of 

 the family. It was sent to me in December 1907, by Mr. \V. 

 Evans, of Edinburgh, who found it, I believe, in April 1906. 



Text-book of Petrology, by F. H. Hatch. London : Swan Sonncn- 

 schein. 5th edition, 1909. 404 pp., 7/6 net. 



The scope of this work is perhaps best described by its sub-title — ' A 

 summary of the modern theories of Petro genesis, a description of the rock- 

 forming minerals, and a synopsis of the chief types of the igneous rocks and 

 their distribution as illustrated by the British Isles.' So many additions 

 have been made to our knowledge of British Petrology in recent years 

 that the present edition of Hatch's well-known text-book has been 

 practically entirely re-written, and besides several new illustrations, the 

 present volume contains many new features. These include a fuller list 

 of references to literature, more complete lists of chemical anal^^ses, the 

 separation of the part dealing with the classfication of rock-types from 

 that dealing with their distribution, and a Table for the Determination of 

 the Chief Minerals of Igneous Rocks in thin section. There is a ver}' good 

 index. 



Radioactivity and Geology, by Prof. J. Joly. London : Constable & 

 Co. 287 pp., 7,6 net. 



Most of those who were fortunate cnougii to squeeze in the crowded 

 lecture theatre at the Dublin Meeting of the British Association, and hear 

 Prof. Joly's presidential address to Section C, as well as those who were 

 left outside, hoped that his address would eventually appear in a more 

 extended form. This hope has been realized, and the book is before us. 

 There is no doubt that the author takes a foremost place in the application 

 he has made of the recent discoveries in radioactivity, to geological science. 

 It is quite possible that geologists have been too hasty in forming generalisa- 

 tions as to the influence of the properties of radioactive elements upon 

 such subjects as the age of the earth, etc., and even Prof. Joly admits that 

 his book contains much that is speculative. Still, if his observations and 

 conclusions were not published, they could not be discussed and criticised, 

 and progress would be slow. As it is his views are carefully and clearly 

 expressed, and no one more than the author will welcome a conscientious 

 and serious criticism of the ideas put forward. No doubt as time goes on, 

 views will change as to the importance of the radioactive elements in the 

 history of our planet ; but, nevertheless, Prof. Joly will always receive 

 credit for his pioneer work in a difficult direction. Amongst the subjects 

 discussed are the foundations of Radioactive Science ; Lhiderground Tem- 

 perature and Radioactivity, the Instability of the Earth's Crust ; Moun- 

 tain Structure ; the Interior of the Earth ; the Age of the Earth, etc. 



Naturalist 



