228 Reviews — F. Ridley's Study of Rocks. 



Already has Dr. Hayden conferred a great boon on geologists by 

 the results (published by the Department of the Interior) obtained 

 by his colleagues and himself during their explorations for some 

 years past of the Western Territories, one portion of which was 

 examined and described by Dr. Hayden eighteen years ago. 



The publications of the Survey during the last year have been 

 both numerous and important, including the magnificent Atlas of 

 Colorado, in twenty sheets (noticed in Geol. Mag. Dec. II. Vol. V. 

 1878, p. 365). 



The tenth annual report of 300 closely-printed pages, with 80 

 maps, plates and sections, will soon be followed by the eleventh, a 

 portion of which is already printed, and this again by the twelfth, 

 for which the materials are ample and of great interest, embodying 

 the full details of which the present pamphlet is only a preliminary 

 report. 



It is to be hoped that no unforeseen circumstances will prevent the 

 progress of the survey of this remarkable country, which even at 

 present has been so graphically laid before us by Dr. Hayden, and 

 that the liberal aid of the United States Government will be con- 

 tinued towards the final completion of the work so ably begun and 

 so energetically carried out, — a work, the value of which, whilst it 

 is of such national importance, is also fully appreciated by European 

 geologists. J. M. 



III. — The Study of Eocks. An Elementary Text Book of Petrology. 

 By Frank Butley, F.G.S. 8vo. pp. 319. (London : Long- 

 mans & Co., 1879.) 



BY the publication of this handy little volume, the author has 

 supplied the want that has for some time been felt by all 

 geologists, whether learners or workers, of a text-book comprising 

 within a moderate compass the more essential information con- 

 cerning the minuter phenomena of structure and association of 

 minerals in rock masses, which it is now customary to distinguish 

 as petrology or lithology, and which the student has had up to the 

 present time to gather, often with considerable labour, from the volu- 

 minous pages of Zirkel, Bosenbusch, and other Continental writers. 

 Although the greater part of the work is devoted to the description of 

 microscopic structure in minerals, the practical details of preparation 

 of thin sections and other methods of manipulation, the larger 

 aspects of the subject are not neglected ; the first forty pages being 

 devoted to a brief but clear description of the phenomena observed 

 on the large scale in the field — including well-illustrated definitions 

 of the terms employed in geological surveying; the methods of 

 representing formations upon maps ; the rules to be observed in 

 collecting specimens, and smaller details of outdoor work. The 

 art of making thin sections of rocks is very completely described, 

 several new points, the results of the author's experience, being 

 given for the first time. The descriptions of individual minerals, 

 and the manner in which they group into rocks, are given in 

 sufficient detail for all the practical purposes required by the 



