REVIEWS PHYSICAL GEOLOGY, ETC. 118 



" It would be a great comfort to a proportion of the geological popu- 

 lation, if the different formations were as clearly distinguishable on the 

 ground as they often are on a map, by different colours, aided by numbers 

 or letters, for the use of the colour-blind. If to this, in the economy of 

 Nature, it had so happened that no species had been permitted to stray 

 from its own formation into the next in succession, the benefit would have 

 been much enhanced, for to those with keen eyes for form, the finding 

 of any single fossil would be sufficient to mark the place in the geological 

 scale of any given formation. Then we should have a perfect and orderly 

 symmetrical accuracy of detail, so that he who runs may read. But it 

 so happens that this is not the case, for Nature loves variety, and 

 performs her functions in various ways, and thus it happens that in 

 certain cases the dividing lines between two formations, if wo follow 

 them far enough, are sometimes difficult to determine." 



The Author has also incorporated in this edition some of the illus- 

 trations and the main points of the matter of his charming little book 

 on the " Glaciers of North Wales." Of other new plates, the most 

 useful are those of the characteristic fossils of the British strata, 

 arranged by Mr. Etheridge, and drawn by Mr. Sharman. 



W. J. H. 



CasselVs Natural HUtory. Edited by P. Martin Duncan, M.B., (Lond.,) 

 F.R.S., F.G.S., etc., Vol. I., small 4to. Cassell, Petter, and Galpin, 

 London, Paris, and New York. 



Few publishers in these times have done more to advance the cause 

 of popular education and recreation than the Messrs. Cassell, and 

 the important work of which the above is a splendid instalment bids 

 fair, when completed, to be one of the most valuable contributions of its 

 kind. The Naturalists under whose care it has been produced ave all 

 men of established reputation, and while the subject has been treated 

 popularly it has not in any way suffered scientifically. The volume 

 before us is devoted to the higher vertebrates, " Apes and Monkeys " being 

 done by the accomplished editor, " Lemurs" by the same, in conjunction 

 with Dr. Murie, F.L.S., F.G.S., &c, and "Chiroptera and Insectivora '' 

 by Mr. "W. S. Dallas, F.L.S. Adopting a principle similar to that laid 

 down by Mr. Herbert Spencer, in his famous Essay on Education, that 

 "as grammar was made after language, so ought it to be taught after 

 language ; an inference which all who recognize the relationship between 

 the evolution of the race and that of the individual will see to be 

 unavoidable," the editor, in his preface, thus describes the method pursued : 

 — " The plan of this work is not to open with a classification of animals, 

 the majority of whose names and shapes are entirely unknown to the 

 reader, but to describe the shape, nature, and habits of groups of crea- 

 tures, and then, when they have become familiar, to arrange and classify 

 them. For the same reason an introduction, dealing with the nature 

 and importance of natural history studies, with the abstract ideas of 

 classification, and with the explanation of the necessity of dividing 



