JXILT 17, 1914] 



SCIENCE 



tm 



tive importance of the alkali and lime-soda 

 feldspars. For aphanitic and glassy rocks this 

 is determined from the norms, from which the 

 average composition of the lime-soda feldspar 

 can be calculated. Distinctions between potash 

 and soda-rocks are also made. 



The granular or phaneritic rocks are treated 

 on the assumption that in most cases their min- 

 eral composition can be approximately deter- 

 mined. The aphanitic and glassy rocks which 

 are chemical equivalents of the phanerites are 

 classed with them, and their equivalence is de- 

 termined through the norms. The limits of 

 divisions in the quantitative system being 

 vague, Iddings has assigned boundaries by 

 quantitative factors which are the same as or 

 similar to some of those used in the quantita- 

 tive system. This involves restricting and 

 redefining of many current terms, but where 

 an old group name, such as andesite, is in 

 question, Iddings has projwsed new names for 

 certain new divisions of the larger and older 

 group. 



While most of the names in current use are 

 retained, Iddings gives precision to many of 

 them, and supplements them by many new 

 ones. As he has been guided by definite prin- 

 ciples, several of which are new in their appli- 

 cation to mineralogical systems, Iddings has 

 practically made a new petrographic system. 

 The reviewer believes that a large proportion 

 of the new propositions will be welcomed by 

 most petrographers of wide acquaintance with 

 igneous rocks as corresponding, at least ap- 

 proximately, to changes in the old system 

 which they have long regarded as necessary. 



The way in which Iddings has subdivided 

 older groups and supplied new terms may be 

 illustrated by a few examples. Three kinds of 

 dacite are recognized, each characterized by its 

 average or normative plagioclase. Oligoclase 

 dacites are called ungaite; those with andesine 

 are called shastaite, and those with labradorite, 

 tandaite. Oligoclase andesite is distinguished 

 from andesite proper as Tcohalaite, while ande- 

 sine basalt is called hawaiite, as distinct from 

 basalts of labradorite feldspar. 



A very valuable feature of the book is the 

 71 tables of chemical analyses of rocks (nearly 



1,100 in all) arranged to show the composition 

 of the new systematic divisions. The norm 

 and quantitative classification of each rock 

 are also given, and a general correlation of the 

 mineralogical and quantitative systems is 

 clearly expressed by the tables. Many dia- 

 grams also serve to show the relations of the 

 two systems. 



Part II. of this volume is a review of what 

 is known concerning the occurrence and dis- 

 tribution of igneous rocks. It is based on 

 personal examination of the extensive litera- 

 ture cited, and the magnitude of the task of 

 preparation for this discussion will be ap- 

 preciated only by those who have made some 

 similar study of original sources. This is not 

 a theoretical discussion of petrographical prov- 

 inces, but an attempt to present the facts of 

 our present very imperfect knowledge of the 

 geographical distribution of igneous rocks. 

 It is significant that Iddings, after this re- 

 view, concludes that " it is too soon to attempt 

 to define the area of any petrographical prov- 

 ince. The data are insufficient for a complete 

 definition or description of any one province 

 . . ." (p. 351). 



The distribution of rocks is presented by 

 means of maps of continental areas and a 

 systematic review of the rocks described from 

 various districts. 



The discussion begins with the rocks of 

 North America as they occur in large prov- 

 inces. Following the geographical treatment 

 is a preliminary discussion of petrographic 

 provinces suggested and a description of their 

 individual characteristics, illustrated by dia- 

 grams. 



The chemical composition of rocks of certain 

 areas is shown by 65 tables containing 1,260 

 analyses, giving norms, etc., as in tables of the 

 systematic part. 



Whitman Cross 



Allen's Oommercial Organic Analysis. Vol. 

 VIII. Fourth edition. Edited by W. A. 

 Davis and Samuel S. Sadtler. Philadel- 

 phia, P. Blakiston's Son & Co. 1913. Pp. 

 X -\- 696. Price, $5.00 net. 

 Allen's " Commercial Organic Analysis," in 



