Oct. 25, 1888] 



NATURE 



61 



able strata are characterized by dry valleys and few 

 water-courses, while the impermeable beds support 

 abundant streams. 



The relations of disturbed strata, of anticlinals and 

 synclinals to valley and hill, are duly noted ; and it is 

 pointed out how the flow of rivers is determined by the 

 lie of the land when it is upraised from beneath the sea- 

 level, and that in few cases are their courses directed by 

 faults or fractures. The authors explain the recession of 

 escarpments by the undermining or undercutting of softer 

 beds and the production of landslips ; and they note the 

 influence of lateral streams in eroding these softer strata 

 at the foot of the hills, a subject illustrated by reference 

 to the Wealden area and other districts. 



Little is said about marine denudation, for the action 

 of the sea is essentially limited to the destruction of 

 cliffs along its margin, and to the formation of marine 

 platforms. Concerning great " plateaux of abrasion," or 

 so-called "plains of marine denudation," the authors 

 express their opinion that it would be wrong to attribute 

 their formation exclusively to the sea, for they consider 

 that the prolonged action of sub-aerial forces is to reduce 

 the land to a level. Nor do the authors attribute great 

 excavating power to glaciers. In their opinion these 

 icy agents occupied and modified old valleys, and have 

 not always effaced the pre- Glacial alluvial deposits ; and 

 they see little evidence of post-Glacial erosion. In these 

 respects their observations are based on local and 

 limited evidence ; for in this country, although the main 

 features were marked out in pre-Glacial times, there is 

 abundant evidence of denudation by glacial action, and 

 subsequently in times when the ice had done its work. 



The authors have clearly pointed out that the topo- 

 graphical features are as a rule in direct relation with the 

 geological structure ; indeed, the form of the ground is 

 one of the most important guides to the field-geologist in 

 his delineation of the superficial distribution of the rock- 

 masses. Nevertheless, in the explanation of the origin of 

 our scenery, there are many points concerning the original 

 extent of each formation, and the changes in texture 

 which the rocks have undergone, that are but briefly, if 

 at all, noticed in this work. In this respect, however, each 

 country must be studied in detail before the complex 

 history of its physical features can be deciphered. 



The present work, as before stated, deals mainly with 

 the mode in which rain and rivers sculpture the surface 

 of the earth. It is an instructive summary of what is 

 known on this subject, supported by original observations 

 and by references to the principal authorities, and illus- 

 trated in a far more sumptuous manner than has ever 

 been attempted in this country. H. B. W. 



OUR BOOK SHELF. 



Eclectic Physical Geography. By Russell Hinman. 

 (New York: Van Antwerp, Bragg, and Co., 1888.) 



To quote the author's preface, "The aim of this book 

 is to indicate briefly what we know or surmise concerning 

 the proximate causes of the more common and familiar 

 phenomena observed at the earth's surface." The book 

 commences with an introduction to the general laws of 

 Nature, in which short outlines of the properties of 

 matter and the various forms of energy are given. The 



earth is then treated as a planet ; its relation to the sun and 

 stars, and the nature and results of its movements, being 

 described. Next come chapters on the atmosphere, the 

 sea, the land, meteorology ; and finally, the various forms 

 of life. The causes of the movements of the atmosphere, 

 sea, and land, and their respective effects, are all clearly 

 stated. Brief outlines are given of the gradual disintegra- 

 tion of terrestrial rocks, and the subsequent transporta- 

 tion and accumulation of the products. Fossils and 

 their teachings also receive attention. In short, nothing 

 of importance has been omitted. 



The general plan of the book bears a considerable 

 resemblance to that suggested by the syllabus of the 

 Science and Art Department's course of elementary 

 physiography, and with a teacher to extend the preli- 

 minary chapter on the forms of energy, would form an 

 admirable text-book for that subject. The order in 

 which the subjects are taken is practically the same, and 

 is obviously the most natural and rational. 



The chapters on the forms of life and their distribution 

 will prove of special interest to young students or general 

 readers. There is a good outline of the development 

 theory, and of what we know of man from prehistoric 

 times. 



The book throughout is illustrated by a great number 

 of drawings, maps, and charts, which not only beautify 

 but illustrate the text in a most admirable manner. The 

 charts are drawn on three different systems of projection, 

 each system being applied where it is most suitable ; and, 

 what is very important, the different systems are fully 

 explained. A book like this cannot fail to impress the 

 reader with a due sense of the importance of diagram- 

 matic representation in facilitating description. The 

 various sectional drawings are especially valuable in 

 this respect. 



The book thoroughly deserves the highest praise, and 

 as an introduction to the study of science must certainly 

 rank amon^r the best. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he under- 

 take to return, or to correspond with the writers of, 

 rejected manuscripts intended for this or any other part 

 of Nature. No notice is taken of anonymous communi- 

 cations.] 



Prophetic Germs. 



Pkof. Ray Lankester has mistaken me. When I said in 

 my last letter of October 8 that "all organs whatever do 

 actually pass through rudimentary s'.ages in which actual use is 

 impossible," I referred specially to the embryological develop- 

 ment of the individual. This is a fact which cannot be denied. 

 But on the Darwinian hypothesis this fact applies equally to the 

 birth of species — which are nothing but the passing results of 

 individual variation. If true now of all individuals, it must, on 

 that hypothesis, ha\e been true of them for all time. 



Inheritance is no explanation of this fact. It is merely one 

 part of the fact separately stated. Neither is " correlation of 

 growth " any explanation of it. This, again, is a mere phrase 

 stating in another form the very fact which it pretends to explain. 

 All organic growths are "correlated." But with what? First, 

 with each other ; and, secondly, with some combined use, which 

 invariably lies in the future when such growths begin. " Corre- 

 lation of growth " is the law under which " prophetic germs " 

 begin to be developed ; and this prophetic character becomes 

 all the more marked in proportion as we carry back existing 

 forms of life to the forms which were primaeval. It is a favourite 

 idea among the disciples of Darwin that the embryological de- 

 velopment of individuals represents in epitome the whole history 

 of organic life. I do not see why they should object to it when 

 it leads us to the conclusion that the whole organic world must 

 have begun in germs which were prophetic — that all organs 

 must have come into being before they could be used. 



Argyll. 



