764 



SCIENCE. 



[N. S. Vol. IV. No. 99. 



ficient basis to construct a revolutionary theory 

 upon. 



In the present pamphlet the author discourses 

 at length upon the well-known fact that in all 

 vertebrates there is an embryonic period at the 

 close of which the anlages of all are present, 

 but not yet differentiated. This stage he calls 

 the 'critical stage,' and he has tabulated the 

 condition of the principal structures in various 

 vertebrates at this stage. This table is a wel- 

 come addition to our embryological conveni- 

 ences. 



"We have been unable to see that the elemen- 

 tary facts, which the author has collated, are 

 anything more than what is commonly taught be- 

 ginners in embryology, nor to recognize that they 

 afford any arguments to support the author's 

 theory of 'antithetic generation.' The estab- 

 lished conception that the embryo is designed 

 to provide undifferentiated tissue for develop- 

 ment rests undisturbed, and offers a sufficient 

 interpretation of embryos, without the interpo- 

 lation of an antithetic hypothesis. 



The note of personal exultation predominates 

 in the pamphlet, and the author closes with the 

 following words : ' ' All the things mentioned 

 above, and many more, are in agreement with 

 the view of an antithetic alteration as underly- 

 ing Metazoon development and — ^Avhere are the 

 facts that are opposed to it?" And echo an- 

 swers — 'where?' C. S. M. 



A Handbook of Bocks for use without the Micro- 

 scope. By James Furman Kemp. With a 

 Glossary of the names of rocks and of other 

 lithological terms. 



This little book is arranged to meet the 

 special needs of those ' engaged in ordinary 

 field work or in mining or engineering enter- 

 prise,' and to present for their use the main 

 facts of petrography in a convenient, compact 

 and intelligible form. "As the men who nowa- 

 days are engaged in such work or in directing 

 such enterprise usually obtain their preliminary 

 knowledge at one or other of our technical 

 schools or colleges, the book will prove of 

 especial value to students in such institutions to 

 be used for private reading in connection with 

 their lectures and demonstrations. A thorough 

 knowledge of the science of petrography, as of 



the allied sciences, botany or zoology, can, 

 only be obtained by the continuous use of the 

 microscope ; the book, therefore, does not pre- 

 tend to be a complete petrographical teatise, 

 but for the purpose of the class of students for 

 whom it is intended it contains an admirable 

 presentation of the subject. 



The various rock-forming minerals are first 

 described and the principles of petrographical 

 classification explained. Five chapers are then 

 devoted to the Igneous Rocks, The student's 

 attention is especially directed to the chemical 

 composition of the several rocks, a series of 

 analyses of each group being presented and 

 commented upon. The mineralogical composi- 

 tion and relationship of the rocks of this class 

 are excellently summed up in a tabular form on 

 page 18, and are also represented graphically 

 by means of diagrams which, however, would 

 be rendered clearer if drawn to a larger scale. 



The aqueous or sedimentary rocks are then 

 taken up and finally the processes of metamor- 

 phism are explained and the principal represen- 

 tatives of the group of the metamorphic rocks 

 are described. 



It seems, however, unfortunate that the au- 

 thor has seen proper to include among the 

 metamorphic rocks all the products of ordinary 

 atmospheric weathering and decay, so that 

 common clay, if a residual product, is classed as 

 a metamorphic rock. This stretching of Lyell's 

 original definition of metamorphism to include 

 all alteration products of whatever kind is 

 hardly advisable. The products of heat and 

 pressure and those of ordinary superficial 

 weathering are too diverse to be properly in- 

 cluded in the same class, even if one were not 

 willing to go so far as Prof. Dana and eliminate 

 from the class of metamorphic rocks all those 

 rocks which are products of alterations which 

 take place at ordinary temperatures. 



Appended to the book is an excellent glossary 

 of rock names, which will prove of great value 

 to beginners as well as to more advanced .stu- 

 dents, for, as Prof. Kemp observes : ' ' One 

 only needs to compile a glossary to appreciate 

 what numbers of unnecessary and ill-advised 

 names for rocks burden this unfortunate branch 

 of science and to convince one that the philo- 

 logical petrographer comes near to being the 



