40 



SCIENCE. 



[Vol. L, No. 2. 



Ion? The question is easily answered. All these minerals have 

 once been embedded in the granitic gneiss which is the principal 

 rock of the region" (and which weathers readily). . . . "In weath- 

 ering, the difficultly decomposable precious stones have not been 

 attaclved, or attacked only to a limited extent: they have there- 

 fore retained their original form and hardness. When in the 

 course of thousands of years, streams of water have flowed over 

 the weathered rock, the softer constituents have been for the most 

 part changed into a line mud, and as such washed away, while 

 the hard gems have only been inconsiderably rounded and little 

 diminished in size. Thecurrentof water, therefore, has not been 

 able to wash them far away from the place where they were ori- 

 ginally embedded in the rock ; and we now find them collected in 

 the gravel-bed, resting for the most part on the fundamental rock 

 which the stream has left behind, and which afterwards, when 

 the water has changed its course, has been again covered by new 

 layers of mud, clay, and sand. . . . Of all the kinds of stones which 

 are used for ornaments, there are both noble and common varie- 

 ties, without there being any perceptible difference in their chem- 

 ical composition. The most skilful chemist would have difficulty 

 in finding, in their chemical composition, the least difference be- 

 tween corundum and sapphire or ruby; between common beryl 

 and emerald; between the precious and common topaz; between 

 the hyacinth and the common zircon; between precious and 

 common spinel: and every mineralogist knows that there are 

 innumerable intermediate stages between these minerals which 

 are so dissimilar, though absolutely identical in composition. 

 This gave the old naturalists occasion to speak of ripe and un- 

 ripe precious stones. They said that in order to ripen precious 

 stones the heat of the south was required. This transference of 

 well-known circumstances from the vegetable to the mineral 

 kingdom is certainly without justification. It points, however, 

 to a remarkable and hitherto unexplained circumstance ; namely, 

 that the occurrence of precious stones is, with few exceptions, 

 confined to southern regions. . . . Another remarkable fact in 

 connection with precious stones is, that most of those that come 

 into the market are not found in the solid rock, but as loose 

 grains in sand-beds. True jewel-mines are few, unproductive, 

 and easily exhausted. From this, one would be inclined to sup- 

 pose that precious stones actually undergo an ennobling process 

 in the Avarm soil of the south." 



To the writer of this note, it seems more reason- 

 able to suppose that the greater abtindance of noble 

 gems in southern climates should be attributed to the 

 more active and thorough-going disintegration which 

 occurs in those regions, and to the consequent — com- 

 paratively speaking — enormous accumulation and 

 concentration of the precious minerals, as above sug- 

 gested. Other things might be far from being equal, 

 and yet the chance of finding a stoue of price be 

 greater in a heap of ten thousand rough jewels than 

 in a collection which contains biit a few score. 



Bussey Institution. F. H. SXOKEK. 



The November aurora in California. 



Auroras are exceedingly rare phenomena in south- 

 ern California; yet Ave had the pleasure of witnessing 

 one Nov. 17, at which time a great electric storm 

 raged over North America and Europe. The photo- 

 graphic traces during the time from Nov. 10 to Nov. 

 20 are very interesting; as they have preserved a per- 

 fect record of the twitchings and jerkings, large and 

 small, fast and slow, to which the magnets were sub- 

 jected during this time. 



A slight sliock of earthquake was reported here 

 on Jan. 23, about 5.20 p.m. I was on the street, and 

 did not feel it; and so far as I can detect no harm 

 was done at the observatory, Makclts Baker. 



Los Angeles, Cal., Jan. 26. 



TRYON'S CONCHOLOGY. 



Structural and systematic conchology : an introduction 

 to the study of the MoUusca; by George W. Try- 

 on, Jr. Vol. I. Philadelphia, the author. 1882. 

 8 4- 312 p., cuts, 22 pi. 8°. 



We have received the first volume of Mr. 

 Tryon's new work (to be completed in three 

 volumes), intended as an introduction to the 

 study of the mollusks. This portion consists 



of some general considerations, a description 

 of the anatomj', habits, and economj^ distribu- 

 tion in space and time, notes on nomenclature, 

 classification and collection, of mollusks. As- 

 sistance in paleontological matters has been 

 rendered bj' Prof. Angelo Heilpriu. The work 

 is well printed and bound ; but the plates, 

 though not so bad as in the ' Manual ' of the 

 same author, contain mostly- inferior render- 

 ings from old and familiar figures, produced 

 by processes which cannot lie made to jield 

 really good results. The map is very badly 

 drawn, and besides this, through ' overlaying,' 

 resulting from folding and inferior or excessive 

 ink, has become nearlj- illegible. Mr. Tr3'on 

 frankly' disclaims authorship for his compila- 

 tion, which is derived almost wholl}' from 

 Woodward's well-known 'Manual,' and the 

 earlier parts of Dr. Paul Fischer's ' Manuel 

 de conchjiiologie/ now in process of publi- 

 cation. Since both these works are accessi- 

 ble at a total price less than that of the first 

 volume of Mr. Tr^'on's book, it is not clear 

 why the latter should exist. Perhaps the fu- 

 ture volumes will explain. 



Meanwhile we do not feel that any very 

 warm welcome should be extended to a work 

 of compilation so destitute of perspective as 

 this. Though not what the author would have 

 made it had Lov^n's work on the dentition of 

 mollusks appeared ten years earlier, AVood- 

 ward's book is nevertheless a thoron'ghlj- co- 

 herent manual, in which the parts retain proper 

 proportions to each other and to the whole. 

 There are manj' statements in it which are now 

 obsolete, or supplemented by more precise, 

 fuller, or more accurate information. Groups 

 not recognized by Woodward ha\'e attained 

 their majority', and no longer train timidly in 

 the leading-strings of a few bold specialists. 

 The study of embr^'ology, histology, and gen- 

 eral anatomy, has entirely changed the situa- 

 tion so far as the point of view is concerned ; 

 but the great merits of Woodward, as origi- 

 nally' published, are as conspicnous as ever. 

 The work of Dr. Fischer is directly on Wood- 

 ward's lines, and embodies of course much of 

 his information ; but it is not a mere revision, 

 an ill-considered conglomeration Hke that of 

 Tate, nor such a compilation as the present one 

 of Tr^'on's. Silk and leather are good in their 

 places ; but man does not patch one with the 

 other, or, doing so, repents of it. Mr. Tryon's 

 first volume appears to us to resemble a mosaic 

 of granite, chalk, precious stones, and mud, 

 which is not delightful to the eye, neither will 

 it wear. The work of the last twenty years in 

 general, except so far as embodied in the ex- 



