100 



SCIENCE 



[N. S. Vol. XL. No. 1020 



■woods of northern Minnesota, particularly in 

 the Eainy Eiver country. These have been 

 years of abundance of the snowshoe rabbit 

 also. The latter have been so numerous that 

 they did great damage by girdling small trees, 

 and the quantity of brush they ate ofE was 

 simply amazing. As one of our rangers put 

 it, " The rabbits in my district have eaten up 

 the brush this winter, and if they increase any 

 more they'll probably start logging next year." 

 The rabbits are rapidly dying off in certain 

 districts this year. 



Ordinarily the black fox is a larger and 

 stronger individual than his red brother. This 

 in itself may have significance. 



Is it unreasonable to assume, in view of the 

 foregoing facts, that a plenteous supply of the 

 food most palatable to the red fox has some 

 influence at least in strengthening the tend- 

 ency of this animal to produce dark-colored 

 specimens, in other words to cause melanism ? 



It is true that some of the increase in the 

 proportion of dark foxes may be due, and 

 probably is due, to the coming in of dark 

 specimens from more northern localities in 

 Canada, following up the abundant mouse 

 and rabbit crop. No locality, even in any of 

 the adjoining portions of Canada, however, 

 has a much higher relative proportion of sil- 

 ver foxes than is ordinarily found along the 

 Eainy Eiver. 



In view of the farming experiments now 

 under way with dark foxes, I should welcome 

 a discussion of this point, which is coming to 

 have economic importance. 



Wm. T. Cox 



State Toeester of Minnesota 



SCIENTIFIC BOOKS 

 Igneous RocTcs. By Joseph P. Iddings. Vol. 



II., Description and Occurrence. New 



York, John Wiley & Sons. 1913. 8vo. Pp. 



xi -|- 685, 20 figures and maps. 



The first volume of Iddings's treatise on ig- 

 neous rocks, dealing in the abstract with their 

 composition, texture, mode of occurrence, 

 origin and classification, appeared in 1909 and 

 was reviewed in Science, Vol. XXX., pp. 408-- 

 411, 1909. The work is now complete with this 



second volume, which presents a systematic 

 description of the rocks and a review of their 

 known distribution and association in all parts 

 of the world. This volume is of the greatest 

 importance to petrographers, for in no other 

 work in any language is there such an exten- 

 sive and judicial analysis of the vast literature 

 of petrography. Iddings has succeeded won- 

 derfully in his difficult task, but it is clear that 

 the time is rapidly approaching when each of 

 the great subjects, systematic description, 

 mode of occurrence and world distribution, of 

 igneous rocks, must be fully treated by itself, 

 unrestricted by the limitations of a general 

 work. 



The markedly original features of Iddings's 

 book make it unusually desirable that the 

 reader should familiarize himself with the au- 

 thor's purpose and plan which are outlined 

 in the preface. From this statement it may 

 be well to quote certain passages, as follows: 



" Since the fundamental need of petrology 

 at this time is a correct understanding of the 

 constitution or composition of igneous rocks 

 it has been the purpose of this treatise to em- 

 phasize the chemical and mineral character- 

 istics in their description. For this reason 

 chemical analyses of rocks, transformed into 

 possible mineral compounds, have been made 

 the foundation on which the systematic de- 

 scription of igneous rocks has been con- 

 structed; that is, they have been employed as 

 a basis of definition and of correlation of 

 rocks that differ in texture and to a greater or 

 less extent in apparent or actual mineral com- 

 position. Igneous rocks have been treated as 

 though they were portions of continuous series 

 of mixtures of mineral compounds varying in 

 numerous ways, and not as specific though 

 somewhat ill-defined compounds possessing 

 individual entities to be reckoned with in their 

 grouping or classification" (page iii). 



" The purpose of the second part of the book 

 has been to present a brief sketch of the dis- 

 tribution of igneous rocks throughout the 

 earth so far as now known, in order to lay the 

 foundation for a study of possible petro- 

 graphical provinces in different regions, since 

 much investigation of these rocks in all re- 



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