

Geology and Mineralogy. 63 



sun. The present thermal condition at the earth's surface was 

 developed during the Tertiary period and was fully attained at 

 the beginning of the Pleistocene period — a date, geologically 

 speaking, so recent that the time which has since elapsed may 

 perhaps be estimated as but one-fiftieth of the time which elapsed 

 since the beginning of the Palaeozoic age. We, therefore, may 

 further conclude that our sun only comparatively recently entered 

 its yellow stage, and we may, without committing a great error, 

 consider that it has now passed -f of its life as a luminous and 

 heating star and that it has still -| before it." In the course of 

 the discussion the chief facts in evidence regarding variation in 

 climate during geological time are brought together in concise and 

 logical form, and are clearly stated. We think the author is 

 incorrect in assuming that " the supposition of a formerly greater 

 amount of carbonic acid in the atmosphere can now no longer be 

 seriously discussed." h. s. w. 



6. Geological Biology ; an introduction to the geological history 

 of organisms, by Hexey S. Williams, pp. 395, figs. 1-150. New 

 York, 1895. (Holt & Co.) — The problems of biology, regarded 

 as specially geological in this treatise, are those concerning the 

 history of organisms, their relations to time and varying condi- 

 tions of environment, and the laws of the modification of characters 

 and the acquirement of differences. As is stated in the preface, 

 "it is evident upon reflection that the biologist proper, who deals 

 alone with the organisms now living upon the earth, must rest 

 with a theoretical interpretation of the laws of evolution. To the 

 geologist the records of evolution are open for direct examination, 

 and geological biology is a scientific treatment of the observed 

 facts of evolution." With this idea in mind the author has put 

 together in systematic form discussions of some of the chief prob- 

 lems desirable as preparation for serious work in paleontological 

 investigation. The general subjects elaborated are the geological 

 time-scale, its divisions, its nomenclature and the principles of its 

 formation, and estimates of the length of geological time ; fossils 

 and their interpretation; geographical distribution; the species; 

 the organism ; principles of classification, etc. 



In the treatment of special topics, such as the modification, 

 acquirement, plasticity and permanency of characters, typical 

 series and groups of organisms are selected for detailed examina- 

 tion, in order to illustrate the exact meaning of the principles 

 involved. The book, as a whole, is a much needed introduction 

 to the study of the history of organisms for the specialist, and is 

 an enunciation of general principles for those looking for a com- 

 prehensive statement of the chief facts in the case. It covers a 

 field heretofore covered by historical geology, which in the rapid 

 differentiation of sciences bids fair to take a place of its own as 

 organic, in contrast to inorganic, geology. 



7. Mikroskopisehe Physiographie der massigen Gesteine von H. 

 osenbusch. 3d ed. enlarged and revised, 8vo, first half, pp. 



552. Stuttgart, 1895. — The great impulse which the science of 



