82 Reviews — Presticich's Geological Text-Book. 



folding maps, three sets of folding coloured sections, and no fewer 

 than 218 woodcuts (many of which are specially prepared for the 

 present work) adorn and make bright its pages, and render good 

 service in the elucidation of the author's views. 



Professor Prestwich, in his preliminary remarks, observes that 

 among geologists two schools have arisen, " one of which adopts 

 uniformity of action in all time, — while the other considers that the 

 physical forces were more active and energetic in past geological 

 periods than at present." 



" On the Continent and in America the latter view prevails, but 

 in this country the theory of uniformity has been more generally 

 held and taught. To this theory I have always seen very grave 

 objections; and I felt I should be supplying a want by placing 

 before the student the views of a school which, until of late, has 

 hardly had its exponent in English text-books." It must be borne 

 in mind, however, that "the doctrine of non-uniformity must not be 

 confounded with a blind reliance on catastrophes; nor does it, as 

 might be supposed from the tone of some of its opponents, involve 

 any questions respecting uniformity of law, but only those respecting 

 uniformity of action." 



" I myself have long been led to conclude that the phenomena of 

 geology, so far from showing uniformity of action in all time, present 

 an unceasing series of changes dependent upon the circumstances of 

 the time ; and that, while the laws of chemistry and physics are 

 unchangeable and as permanent as the material Universe itself, the 

 exhibition of the consequences of those laws in their operation on 

 the earth has been, as new conditions and new combinations succes- 

 sively arose in the course of its long geological history, one of 

 constant variation in degree and intensity of action." 



Prof. Prestwich very properly points out that, for the student, the 

 first object " should be to study the laws to which the materials and 

 masses he has to deal with are subject, and then to consider what 

 may have been their action under vai'ying conditions in past time." 

 With this object the author has divided his work into four parts : 

 " The first, treating of the composition of minerals and rocks forming 

 the crust of the earth ; the second, the mode of action of geological 

 agencies under existing and under past conditions : while the third 

 and fourth will treat of the succession of the groups of sedimentary 

 strata and of the life thereof, and of some of the theoretical questions 

 connected with the physical conditions prevailing during former 

 periods of the earth's history." The four earlier chapters up to p. 6L 

 comprise a consideration of the constituents of the Earth's crust, 

 which are enumerated and described, and all the numberless forms of 

 rocks resulting from the varying combination of their constituent 

 minerals are discussed and exemplified. 



The mode of action of geological agencies should have commenced 

 at p. 62 ; but Chapter V. is occupied with an account of the " Order, 

 Place, and Range of past Life." This we venture to think might 

 have been held over and formed a part of Vol. II., in which the 

 Life-history of the Earth will be discussed. 



