Jan. 31, 1889] 



NATURE 



315 



with him that "the phases of development which have 

 i^raduplly led up to conceptual thought admit of being as 

 clearly traced as those which have led to any other product, 

 whether of life or of mind"; if I even go further, and 

 confess my belief that mental evolution never will be and 

 never can be independently established, though it may 

 be accepted as a corollary from organic evolution by 

 iliose who are content to remain naturalists ;— this does 

 not lead me to welcome any the less cordially the valuable 

 researches of Mr. Romanes in a very interesting but 

 exceedingly difficult field of investigation. 



C Lloyd Morgan. 



THE MICROSCOPICAL STUDY OF MINERALS 



IN ROCKS. 

 Microscopical Physiography of the Rock-making Minerals : 



an Aid lo the Microscopical Study of Rocks. By H. 



Rosenbusch. Translated and Abridged for use in 



Schools and Colleges by Joseph P. Iddings. Illustrated 



by 121 Woodcuts and 26 Plates of Photomicrographs. 



(New York : John Wiley and Sons. London : Mac- 



millan and Co., 188S.) 

 Hillfstabellen zur mikroskopischen Mineralbestimnumg 



in Gestcinen. Zusammengestellt von H. Rosenbusch. 



(Stuttgart : E. Koch, 1888.) 

 Les Mineraux des Roches. Par A. Michel-Levy et Alf. 



Lacroix. (Paris : Libraire Poly technique, Baudry et 



Cie. 1888.) 



IT has been well said that this is an age of books. 

 With equal propriety it might be characterized as 

 an age of text-books. Indeed, so rapidly do these aids 

 to learning increase and multiply, that it seems almost 

 incredible that any rational proportion can still exist 

 between demand and supply. In works on petrography, 

 the year just passed away has been exceptionally fruitful. 

 From the ponderous tome, replete with detail and 

 illustrated by magnificent plates, down to the superficial 

 shilling primer, we have before us a remarkable series of 

 volumes in which rocks and their constituent minerals 

 are treated from all the most recent points of view. It 

 was in the early months of 1888 that Prof. Rosenbusch's 

 invaluable " Mikroskopische Physiographic," was com- 

 pleted by the publication of the second part of Volume 

 II., and the same year has also witnessed the appearance 

 of Mr. J. P. Iddings's translation of the first volume, on the 

 " Mikroskopische Physiographie der petrographisch wich- 

 tigen Mincralien." The usefulness of this book as a 

 work of reference cannot be over- rated, as will be 

 < acknowledged by all those who have had occasion to 

 i use it. Unfortunately, it has hitherto been sealed to 

 \ those who possessed no knowledge of German, and 

 Mr. Iddings has earned the thanks of English-speaking 

 petrographers in undertaking its translation, a task 

 involving no inconsiderable amount of patient labour. 



In the English edition the book has been slightly 

 abridged, but in doing this the translator has " endea- 

 voured to retain all that appeared essential to a fair 

 general comprehension of the subject, omitting what 

 seemed to be refinements beyond the need of the average 

 student, and for which the advanced student is referred 

 to the original work. Thus most of the historical por- 

 tions have been omitted, as well as the elaborate treat- 



ment of the optic anotnalies of certain minerals, and 

 many notes o\\ European localities ; while a number of 

 notes on American occurrences have been inserted." We 

 cannot help thinking, however, that it would have been 

 an advantage to retain the alphabetical index to petro- 

 graphical literature, which, on account of its complete- 

 ness, forms one of the most valuable features of Prof. 

 Rosenbusch's work. Reference to original sources should 

 be encouraged to the utmost in a students' book. 



Mr. Iddings has added some useful information on 

 allanite, or orthite, as some prefer to name it. According 

 to his researches, carried out in conjunction with Mr. 

 Whitman Cross, the occurrence of this mineral as an 

 accessory constituent of rocks is much more wide-spread 

 than is usually supposed. These authors have shown it 

 to be widely distributed through a great variety of rocks 

 in the United States, it having been found in gneiss, 

 granite, granite-porphyry, quartz-porphyry, diorite-por- 

 phyrite, andesite, dacite, and rhyolite. It is possible that 

 it has sometimes escaped recognition, owing to its resem^ 

 blance in colour and pleochroism, to some varieties of 

 hornblende and biotite. It may, however, be distinguished 

 from the former by its higher double refraction, and from 

 the latter by its larger optic axial angle. 



The translator must be congratulated on the very 

 successful way in which he has rendered the original into 

 clear and concise English, while keeping strictly within 

 the author's meaning ; indeed, were any fault to be 

 found with Mr. Iddings's style, it would perhaps be that 

 he has a tendency to translate too literally. But this is 

 I erring on the safe side. Occasionally, however, he goes 

 to the other extreme, the translation becoming so free as 

 to be inaccurate, as, for instance, when " crystaUitiische 

 Schiefer" is rendered "Archaean formation," so that 

 phenomena of dynamic metamorphism (such as the 

 marginal crushing of crystals, or "cataclastic structure"), 

 that are common to the crystalline schists of whatever 

 age, are thereby limited, inferentially of course, to rocks 

 of Archaean age (pp. 251, 277, 279, 284, 307, 309, 310). 

 The word Sphdrokrystal has been rendered spherulite, on 

 the ground that the latter has become well established in 

 English literature. This is true ; but the word spherulite 

 is equally well known in Germany. On p. 392 of the 

 " Physiographie der massigen Gesteine,'' Prof Roien- 

 busch carefully distinguishes between the meanings he 

 attaches to spherocrystal and spherulite respectively ; the 

 former being applied by him to spherular bodies consist- 

 ing of radially-aggregated fibres of a single mineral {e.g. 

 chlorite), the latter to those imperfectly individualized 

 fibrous bodies so common in vitreous rocks. 



In one or two instances only has Mr. Iddings been led 

 astray by the peculiarities of the German idiom. The 

 most serious of these slips occurs on p. 286, where wq 

 read that, " in the so-called pseudomorphs of cassiterite 

 after orthoclase from Huel Coates, tourmaline and quartz, 

 besides cassiterite, form a principal part of the mus- 

 coz'ite.^' The meaning of the original, which is, it is 

 true, somewhat ambiguously expressed, is, that besides 

 cassiterite, tourmaline, and quartz, muscovite forms one 

 of the principal constituents of the pseudomorphs after- 

 orthoclase from Huel Coates.^ 



' " Auch bei der so^. Pseudoniorphobe von C.'X'-siterit nach Orthoklas von 

 Huel Cites im Kirchspiel St. Agnes, Cornwall, bildet neben Cassiterit, 

 TMrnvalin und Quarz der Muicovit einen Hauptgcmengthsil." 



