726 SCIENCE PROGRESS 



mastered before the detailed study of rocks and fossils is undertaken. It may be 

 questioned, however, whether this dictum will meet with general acceptance. All 

 will agree that attention should be given first to the operations of the natural 

 forces that are ever moulding and transforming the earth's crust but there seems 

 good reason for postponing serious work at stratigraphy, the crown and end of 

 geological research, till the student has a fair acquaintance with both petrology 

 and palaeontology. That stratigraphy is not an elementary department of the 

 science, that can be conveniently yoked with the principles of dynamical geology, 

 is strikingly illustrated by the volume before us ; for it is emphatically not a single 

 textbook which is the joint work of two authors but two distinct textbooks in a 

 single binding. 



In the fifteen chapters on physical geology, which are contributed by 

 Mr. Rastall, the treatment of the whole subject is sound but it is especially 

 effective and up to date when it deals with the processes which can now be 

 observed in operation on the surface of the globe ; we may instance the descrip- 

 tion of the phenomena characteristic of arid conditions, glaciation and volcanic 

 activity. In the more speculative aspects of the subject the author is more open 

 to criticism. In explaining the frequent association of lakes with evidence of 

 glacial action he never alludes to the view which is now widely held that they are 

 in many cases at least the result of differential elevation and depression while the 

 action of running water was suspended by frost or the accumulation of ice. At the 

 same time the different explanations which have been advanced of the occurrence 

 of glacial periods do not receive even a passing allusion. The brief treatment of 

 the igneous rocks is on the whole satisfactory ; but why are the terms " alkaline " 

 and " subalkaline " employed to express the difference between syenite and 

 diorite ? The prefix " alkali- '' has a recognised use as denoting rocks in which 

 felspars containing an appreciable amount of lime are practically absent and in 

 which the pyroxenes and amphiboles are represented by soda-bearing varieties. 

 One would certainly not understand the expression " alkaline rocks '' to include a 

 normal syenite. In concluding the notice of this portion of the book, a word of 

 praise must be given to the excellent reproductions of photographic plates which 

 illustrate in a most effective manner the phenomena described. 



The remaining fifteen chapters which are devoted to the stratigraphy of the 

 British Isles are by Mr. Lake, who must have experienced some difficulty in 

 compressing the subject-matter into the two hundred pages which are allotted to 

 him. It is perhaps for this reason that references to foreign geology are as a 

 general rule absent. Even the fragment of France which regularly appears in the 

 south-east corner of the maps showing the extension of the different formations is 

 always left blank, in spite of the opportunity it affords of indicating the continua- 

 tion of the Wealden anticline across the Channel. We can only hope that this 

 exclusion of foreign stratigraphy points to the early appearance of a work specially 

 devoted to the subject by the same author, who possesses exceptional qualifications 

 for the task. 



In stratigraphy, probably more than in any other department of geology, there 

 is room for difference of opinion and it is natural that there should be a number 

 of points in which Mr. Lake is not in agreement with other authorities. We need 

 not be surprised, for instance, that the Ingleton slates, which Mr. Rastall has 

 given us good reason to believe are of pre-Cambrian age, find no place in the 

 chapter dealing with these early rocks or the map in which the localities where 

 they occur are indicated ; for the independence of the two authors is firmly 

 impressed upon us in their preface. Sufficient stress is hardly laid on the 



