262 Bibliographical Notices. 



beds being referred to the Carboniferous Limestone. The views of 

 Daubree as to the origin of cassiterite and its associated minerals 

 are quoted at some length. 



Physical Geology, of which a brief and inadequate notice has been 

 given above, occupies 436 pages of the entire volume, and no small 

 portion of this, as we have seen, is devoted to the more intimate 

 study of the rocks. Prof. Seeley has, in fact, been deeply bitten by 

 that love of petrology (using this term also to include lithology) 

 which is so characteristic of the present day. We notice here (as, 

 iudeed, throughout the whole of this portion of the work) the results 

 of diligent and careful inquiry carried on in a philosophical and un- 

 biassed spirit. Some crilics might perhaps demur to the general 

 arrangement as being rather complex ; but of the excellence of a 

 large portion of the matter there can be no doubt. Considering that 

 the chief scope of Prof. Seeley's studies has hitherto lain in quite 

 another direction, his grasp of petrological questions is remarkably 

 good. It would be most ungenerous uot to admit this to the full, 

 even though some unimportant errors may be demonstrable. 



The two remaining chapters are devoted to Palaeontology, con- 

 cluding with a review of the succession of animal life. As may be 

 supposed, this portion of the work is full of interest, though parts of 

 it read more like an essay than a text-book. In common with 

 most modern authors, Prof. Seeley considers that existing creatures 

 are the descendants of a long chain of preexisting creatures, and 

 thus Palaeontology becomes the history of the succession of life on 

 the earth. "It begins with a remote past, when the great groups 

 of organisms were already characterized, and many surviving genera 

 were in existence." 



Dealing with the question of the " Origin of Species,'' he points 

 out the logical defect in Darwin's original argument, since that 

 author did not explain the cause of structural variation. Prof. 

 Seeley claims that as far back as 18o2 he had already indicated, in 

 the ' Transactions of the Cambridge Philosophical Society,' that the 

 fundamental active principle in evolution is physiological causation, 

 which, though not uninfluenced by external conditions, is more 

 dependent upon circumstances of function. This view has of course 

 presented itself to most biologists, and some have gone even further 

 to the length of expressing their surprise that, on the whole, the 

 process of structural change has been so slow throughout the suc- 

 cessive ages — so slow, indeed, that some existing forms are almost 

 identical with those of a tolerably remote past. This subject is 

 well treated of under the head of " Persistent Types of Life." The 

 author considers that the direction of physiological variation is always 

 towards increased complexity of structure ; but the direction of 

 variation under external influences is often towards increased sim- 

 plicity of structure. Hence, apparently, the two tendencies serve 

 partly to balance each other. 



The author, bearing in mind that he is writing a text-book, 

 observes that " every fossil, like every plant and animal, must be 

 referred to its ' genus ' and ' species,' and we need to have clear 



