784 SCIENCE PROGRESS 



practical notes are given in Chapter V. on the installation of seismographs, and 

 we are then asked to consider the characters of a record resulting from a shock 

 initiated in a solid isotropic earth. Though such an earth fails to satisfy the actual 

 readings of the instruments, we are not allowed to comfort ourselves with the idea 

 that these readings as yet give us reliable information about earth-shells and 

 variations of density below the surface. 



The most marked recent advance appears to be Galitzin's determination of the 

 epicentre of a shock from observations at one station only (p. 64). The science of 

 seismology, as distinct from seismoscopy, is so modern that Mr. Walker, watching 

 the work of his colleagues in this field of delicate measurement, and observing 

 earthquakes critically on his own account at Eskdalemuir, can look forward 

 confidently to successive editions of his treatise. 



The Petrology of the Sedimentary Rocks. A description of the Sediments 

 and their Metamorphic Derivatives. By F. H. Hatch, Ph.D., and R. H. 

 RASTALL. With an Appendix on the Systematic Examination of loose 

 Detrital Sediments. By T. Crook. [Pp. xiii + 425. With 60 text- 

 figures.] (London : G. Allen & Co., 1913. Price 7s. 6d. net.) 



This book is divided into two portions, of which the first deals with unaltered 

 sedimentary rocks, and the second with the changes such deposits may undergo 

 subsequent to their deposition. 



The first portion is by far the smaller, and treats in a general and brief manner 

 the processes of formation, and the classification of stratified rocks which are 

 arranged under the headings Fragmental, Chemical, and Organic. There is no 

 doubt that for purposes of a text-book it is desirable to draw rather hard and fast 

 lines ; but the division between chemical and organic deposits cannot be definite, 

 and there can never be a strictly logical separation of the two groups. The 

 authors have shown a great tendency to concentrate on the second portion of 

 the work and to treat the metamorphic rocks with conspicuous partiality ; not only 

 this, but metamorphism has been extended to the widest limits placed upon the 

 term by trans-Atlantic workers, and has been made to embrace all rocks except 

 those which have suffered practically no change of any description. This is a 

 departure from the system usually adopted in this country, and is not to be 

 recommended. 



The elementary student and also the more advanced worker will find this book 

 of considerable use, for collected between its covers is a store of information which 

 previously was scattered through varied and often obscure publications. The 

 worker, however, who turns to this book for detailed descriptions of any particular 

 type of sedimentary deposit will be disappointed, for, unlike the mode of treatment 

 adopted for the igneous rocks in the first volume, the sediments are discussed 

 in general with special reference to their mode of origin and subsequent changes. 

 It is true that specific examples are given in many cases, but these examples are 

 too few in number ; and at the same time it is to be regretted that so many have 

 been drawn from distant foreign localities when there are equally good examples 

 which might have been quoted from Britain. 



A most useful Appendix has been drawn up by Mr. Crook on the methods of 

 examination of loose detrital sediments. It is an admirably clear account of the 

 methods usually adopted for the separation of mineral constituents from each 

 other, and it includes data for the determination of the commoner mineral species 

 present in sedimentary deposits. From these data the author might perhaps 



