500 



SCIENCE 



[N. S. Vol. XLIV. No. 1136 



If in the ancient Pacific from long ago, that is 

 from the opening of the Paleozoic on, the denser 

 Sima lay exposed . . . and if that was the site of 

 the permanent abyss, then has the dense material 

 under the Atlantic and Indian oceans been ex- 

 posed through displacement of the lighter salie 

 continents, as if by the drawing back of a curtain, 

 and the existing coincidence of the limits of den- 

 sity with the outlines of the continents and oceans 

 is explained. The former invasions of the sea, 

 which are shown to have spread over what are now 

 land areas, are passing transgressions; the Pa- 

 cific and the continents are permanent, aside from 

 the displacements; the Atlantic and Indian oceans 

 are younger deeps, floored with sima which ap- 

 pears at the surface in consequence of the dis- 

 placements [of the continents]. Thus the prob- 

 lem of permanence is robbed of its contradictions 

 and in essentials is explained. 



The speculative section of the work, occupy- 

 ing 200 pages, thus presents some of the 

 greater problems of geology as the introduc- 

 tion to paleography. Another and in the opin- 

 ion of the reviewer a sounder method is to pro- 

 ceed from the facts of paleogeography toward 

 the solution of those problems. 



As a contribution to the science the latter 

 half of Dacque's work will seem to many the 

 more valuable. In it are assembled the data 

 of sedimentary formations considered as facts 

 appropriate to paleogeographic investigation, 

 estimates of absolute and relative durations of 

 geologic time divisions, and examples of the 

 construction of paleogeographic maps. The 

 facts of stratigraphy and paleontology are ad- 

 mirably summarized, and the assemblage of 

 illustrations constitutes a rich and suggestive 

 reference for students of the subject. 



Bailey Willis 

 Stanford University 



Plant Life. By Charles A. Hall, F.R.M.S. 

 The Macmillan Company, 66 Fifth Avenue, 

 New York, N". Y. Cloth. Pp. 380. Eighty 

 text-figures and seventy-four full-page illus- 

 trations. Price six dollars ($6.00). 

 Professor Hall has already written several 

 books presenting various phases of nature- 

 study in a popular way, so that experience in 

 the field, in the laboratory and in the study 



have combined to make the present volume on 

 " Plant Life " a useful addition to the series. 

 It is addressed, principally, to the amateur 

 botanist and lover of nature, but contains 

 much which should be of interest to teachers 

 of elementary classes. 



The treatment follows the general evolu- 

 tionary order from the lowest plants up to the 

 highest. The excellent descriptions of field 

 characters is an important feature of the work 

 and should enable the beginner to find even 

 the microscopic forms. Interesting bits of in- 

 formation and clever observations afford wel- 

 come material to those who wish to brighten 

 their lectures and laboratory work. 



The headings of the twelve chapters indicate 

 not only the scope of the book, but also what 

 might be expected in the mode of treatment. 

 The headings are : Asexual Plants ; The Devel- 

 opment of Sex in Plants and a Study in Evo- 

 lution; Seaweeds; Fungi and Lichens; Bryo- 

 phytes — Liverworts and Mosses; Pteridophytes 

 — Ferns, Horsetails and Club Mosses ; Phanero- 

 gamia, Flowering Plants; Fossil Plants; The 

 Food of Plants and How they Secure It; The 

 Perpetuation of the Race; The Defences of 

 Plants; Ecology; The New Field Botany. 

 There is a general glossarial index. 



The illustrations are excellent and most of 

 them are new. In addition to eighty text- 

 figures, there are seventy-four full-page illus- 

 trations, twenty-four being from photographs 

 by the author and fifty in color from draw- 

 ings by C. F. Newall. The binding and typog- 

 raphy are in keeping with the high grade of 

 the illustrations. 



Charles J. Chamberlain 



PROCEEDINGS OF THE NATIONAL 

 ACADEMY OF SCIENCES 



The eighth number of volume 2 of the Pro- 

 ceedings of the National Academy of Sciences 

 contains the following articles: 

 1. The Absorption Coefficients of Soft X-rays: 



C. D. Miller, Ryerson Physical Laboratory, 



University of Chicago. 



The numerical constants in the relation be- 

 tween the absorption coefficients, the density, 



