236 



SCIENCE. 



[Vol. XXn. No. 560 



the hand-book of the future. In the matter of termin- 

 ology, one notes with satisfaction the author's precision 

 in the use of such terms as " slate," for instance, as char- 

 acteristic of argillaceous rocks possessing slaty cleavage. 

 The microscopic structure of the clastic rocks is fully up 

 to date. The igneous rocks are treated in the light of 

 the ^studies of the most advanced petrographers. Prof. 

 Geikie, we think, rightly adheres to a simple classification 

 of the igneous rocks into an acidic, intermediate and 

 basic series, since he deems it inexpedient to divide them 

 as does Eosenbusch into an ancient and modern series. 

 Zirkel's error in mistaking plagioclase for sanidine in the 

 andesites of the 40th Parallel Survej^ made known by 

 the work of Hague and Iddings, is noted. 



Prof. Geikie thinks the geological evidence demands 

 " an amount of time not far short of the hundred millions 

 of years originally granted by Lord Kelvin," and he has 

 evidently read Mr. King's admirable paper published this 

 year (see p. 60). 



In the section on Denudation, the competency of 

 meteoric agencies to reduce lands toward a base-level is 

 ably discussed, but the American student who has fol- 

 lowed the advanced studies in geographic evolution pub- 

 lished by Davis and others within the past five years will 

 be somewhat disappointed in the retention of the phrase 

 " plain of marine denudation " for the term "peneplain" 

 adopted by G. M. Dawson and other writers on the great 

 base-level of erosion in North America. Prof. Geikie 

 maintains that the finishing touches in these table-lands 

 of erosion are given by the horizontal planing action of 

 the sea. 



The action of bacteria in producing decay and soils is 

 not mentioned, but this recently discovered geological 

 agent is scarcely missed in the interesting discussion of 

 the geological action of plants and animals. The work 

 accomplished by cryptogamous plants is carefully re- 

 viewed and fully presented. In the discussion of coral- 

 reefs, the views of Darwin, Murray and A. Agassiz are 

 thoroughly presented. Prof. Geikie completes his review 

 of the subject with the statement "that the wide-spread 

 oceanic subsidence demanded by Darwin's theory cannot 



be demonstrated by coral-reefs must now, I think, be 

 conceded." 



The concise use of terms which characterizes the larger 

 part of the work is further illustrated in the case of "lac- 

 colite " proposed by Gilbert for igneous intrusions which 

 " have spread out laterally and pushed up the overlying 

 strata into a dome-shajjed elevation." The laccolites are 

 thus contrasted with the simple "intrusive sheets" or 

 " sills " which have the apjDearance of interbedded masses. 

 This last term for the first time appears as a convenient 

 designation for the numerous thin, interbedded rocks 

 which are sometimes erroneously called laccolites. Prof. 

 Geikie also carefully adheres to the generally accepted 

 use of the term " monocline " as used by the geologists of 

 our western surveys. The part dealing with metamorphism 

 ought to be read by every student of geology. The section 

 on Regional Metamorphism has been much espianded so 

 as to embrace the advances recently made in this im- 

 portant branch of geological science. It is clearly pointed 

 out that igneous rocks as well as clastic beds have been 

 altered into gneisses and schists; and the effects of great 

 pressure are carefully discriminated. 



The. chart of geological periods naturally differs in its 

 main divisions from the plan recently projjosed by the 

 U. S. Geological Siirvey. The pre-Cambrian, including 

 the Algonkian and the Fundamental complex, or all that 

 has up to • within a few years been called Archten, is 

 placed under the head of Primary or Palaeozoic, a posi- 

 tion which is still an undecided matter at least in this 

 country. It seems clear that the Algonkian as now con- 

 stituted is Palsezoic, as Dana has urged; but the "Funda- 

 mental complex" may yet be proved Archfen in the sense 

 in which the word was originally intended. The Quebec 

 group has been dropped, as it should be. The North 

 American Pleistocene glacial periods are described under 

 the head of Champlain, as in the jirevious edition, a sum- 

 mary which seems strange to the student of glacial geol- 

 ogy in this country. 



The book on Stratigraphic Geology is particularly en- 

 riched by abstracts setting forth the recent accessions to 

 our knowledge of the ancient and usually metamorphic 



FOSSIL RESINS. 



This book is the result of an attempt to 

 collect the scattered notices of fossil resins, 

 exclusive of those on amber. The work is of 

 interest also on account of descriptions given 

 of the insects found embedded in these long- 

 preserved exudations from early vegetation. 



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