

July 31, 1890J 



NATURE 



315 



amination of the faecal pellets and of the alimentary- 

 canal, eats the wood-work used in the construction of the 

 filters, and also the hyphae, conidia, &c., of the Fungus 

 Melanonima pulvis-pyriiis. The yi 5-^/// are found to eat 

 away the softer spring wood of the beams, and leave the 

 harder autumn wood of the annual rings standing out as 

 ridges. Consequently one important practical conclusion 

 at which the Rotterdam Commission arrived was that 

 the wooden beams in the filters should be removed, and 

 their place be taken by cement, which would not afford 

 shelter and nourishment to the Crustacea, Fungi, and 

 other organisms. The Report is illustrated by woodcuts, 

 and a plate giving a plan of the Rotterdam water-works, 

 so as to show the connection between the various 

 reservoirs and aqueducts and the course taken by the 

 water in passing through the system. 



W. A. Herdman. 



AMERICAN GEMS. 

 Gems and Precious Stones of North America : a Popular 

 Description of their Occurrence , Value, History, Archceo- 

 logy, and of the Collections in which they exist; also 

 a Chapter on Pearls, and on Remarkable Foreign Gems 

 owned in the United States. Illustrated with Eight 

 Coloured Plates and numerous minor Engravings. By 

 George Frederick Kunz. (New York : The Scientific 

 Publishing Company, 1890.) 



THE general dissociation in Nature of useful and 

 ornamental materials, which has often been com- 

 mented upon, finds nowhere a more striking illustration 

 than in the North American continent. Rich as this part 

 of the globe is in coal, the ores of iron, and of almost all 

 the metals employed in the arts, as well as in all kinds of 

 building materials, yet the value of gem-stones found 

 within its limits is practically insignificant. As the author 

 of the work before us admits, 



" the daily yield from the iron and coal mines, or from 

 the South African diamond mines, or a week's yield of 

 the granite quarries, would exceed in value the entire 

 output of precious stones found in the United States 

 during a year." 



Small though their aggregate value may be, however, there 

 are many facts concerning the variations in character and 

 the mode of occurrence of these interesting and beautiful ob. 

 jects, the gem-stones, which can better be studied in North 

 America than in any other part of the world. Nor could 

 we possibly wish for a more fully informed guide than 

 Mr. Kunz : his skill as a mineralogist is well known, and 

 he has frequently, in his capacity of gem-expert to Messrs. 

 Tiffany and Co., been able not only to reject the spurious 

 but to recognize for the first time the latent capabilities of 

 mineral varieties not previously employed as gems. 

 Since the year 1883, Major J. W. Powell, the Director 

 of the U.S. Geological Survey, has published a valuable 

 series of annual volumes on " The Mineral Resources of 

 the United States" ; and the chapters on precious stones 

 in these reports have been written by Mr. Kunz. 



The book aims at combining the exact information 

 required by the mineralogist with the curious and some- 

 times trivial, but by no means unimportant, lore dear to 

 the collector and the archaeologist. As is fitting in such a 

 NO. T083, VOL. 42] 



work, the typography and illustrations are of remarkable 

 excellence, and reflect the highest credit upon the printers 

 and engravers of the United States ; indeed, it would be 

 hard to find anywhere a volume which combines so 

 many excellences, alike in the paper, printing, plates, 

 and binding. 



Every care has evidently been given to making the 

 scientific part of the work trustworthy ; and we may es- 

 pecially refer to the chapters which deal with the corun- 

 dums, the beryls, and the felspars of the United States, 

 as containing much new and valuable information. The 

 details concerning the silicified (" jasperized ") woods of 

 Arizona given in this book are more complete and satis- 

 factory than any that have before appeared, while the 

 accounts of the pearls and pearl-fisheriesof North America 

 are full of interest. In order to make the work more 

 complete, the twelve chapters on the gems of the United 

 States are followed by two others on the precious stones 

 of Canada and Mexico respectively. Little inore than 

 an enumeration of the gem-stones of the Dominion can 

 be given in the space at the command of the author, but 

 more justice is done to the jades, opals, and obsidians of 

 Mexico. 



The two last chapters deal respectively with the lapi- 

 daries' work performed by the aborigines of North 

 America, and the work of the same kind now being done 

 in the country ; and both chapters abound with curious 

 and interesting facts. The publication of this book 

 cannot fail to call attention to the importance of sys- 

 tematic searches being carried on with a view to the 

 discovery of some of the more valuable gem-stones, in 

 districts where no authentic account of their occurrence 

 at present exists. Collectors, archaeologists, jewellers, and 

 dealers will all find their respective wants anticipated by 

 Mr. Kunz ; and by attention to the methods of discrimina- 

 tion and the detection of fraud which he indicates, will 

 be saved frequent disappointment and much pecuniary 

 loss. J. W. J. 



OUR BOOK SHELF. 



Timbers, and how to Know Them. By Dr. R. Hartig, 

 Professor of Botany in Munich University. Translated 

 by W. Somerville. (Edinburgh: Douglas, 1890.) 

 The original of this little book is the third edition of a 

 small pamphlet entitled " Die Anatomischen Unterschei- 

 dungsmerkmale der wichtigeren in Deutschland wachsen- 

 der Hdlzer," and why the translator should have altered 

 the significance of the title is not explained. In any case 

 it would not be easy to justify the more ambitious title of 

 the English translation, seeing that no additions have 

 been made to the original, and that the original title claims 

 too much. For the book does little more than give in 

 bare outline the more conspicuous features observed on 

 the transverse sections of our common woods ; and al- 

 though this is done fairly well, the treatment is neither 

 exhaustive nor free from defects. 



The only other alterations made by the translator are the 

 additions of an index and a glossary. The former appears 

 adequate and useful, the latter has shortcomings, especi- 

 ally under the headings " bordered pit," " parenchymatous 

 cells," &c. Definitions such as " Vertical resin-duct, on& 

 which runs longitudinally, i.e. parallel to the outside of a 

 stem," are, to say the least, not improved by the additional 

 remark. 



With regard to the actual translation, it is good and 



