384 MR. F. RUTLEY ON THE ORIGIN OP [Aug. 1 894, 



The late John Arthur Phillips, in speaking of the siliceous 

 deposits at Steamboat Springs, Nevada, U.S., remarked that " the 

 fissures, which appear to have been subjected to a series of repeated 

 widenings, such as would result from an unequal movement of their 

 walls, are lined, sometimes to a thickness of several feet, by incrus- 

 tations of silica of various degrees of hydration, containing hydrated 

 ferric oxide and, exceptionally, crystals of iron pyrites. This silica 

 exhibits the ribbon-like structure so frequently observed in mineral 

 veins, and, when examined under the microscope, is seen to consist 

 of alternately amorphous and crystalline bands, enclosing druses 

 lined with minute crystals of quartz." 



Speaking of an older group of fissures, about a mile west of the 

 last-named locality, he adds: — " The silica of this deposit is sometimes 

 chalcedonic and contains nodules of hyalite ; the larger proportion 

 of it, however, although somewhat friable, is distinctly crystalline. 

 The crystals contain numerous liquid cavities, and exhibit the usual 

 optical and other characteristics of ordinary quartz." x 



The foregoing statements prove, I think, quite sufficiently, that 

 deposits of silica may pass from the amorphous into the crystallized 

 condition, and, bearing this in mind, it appears by no means improbable 

 that like changes may occur in the silica which replaces a limestone. 



Mr. Griswold regards the siliceous grains which constitute the 

 Arkansas novaculites as quartz. The specific gravity of Arkansas 

 stone, however, is given by him as 2-648 or, making allowances 

 for the " excess of weight caused by the presence of the heavier 

 elements," 2-643. He adds that " this falls within the limits given 

 for silica in the form of quartz (' Chemiker-Kalender ' for 1888), 

 which places the specific gravity at from 2-64 to 2-66. The specific 

 gravity of novaculite may be a trifle lower than the average for 

 quartz, since some air may remain in the pores of the stone and 

 decrease its weight in water by a small amount." 2 



In order to avoid any error due to the presence of cavities, I 

 reduced fragments of the translucent Arkansas stone to fine powder, 

 and employing the pycnometer and distilled water at 15° C, found 

 the specific gravity to be 2*6441. The weight of powdered stone 

 used was 2^ grammes, and every precaution was taken to ensure 

 accuracy. Mr. Griswold's estimate, 2-643, approximates very closely 

 to this, but in either case it seems that the specific gravity comes 

 rather within the range of chalcedony than of quartz. Prof. J. 

 D. Dana gives the specific gravity of chalcedony as 2*6 to 2-64, 

 which agrees with that of Arkansas stoue, while for quartz he gives 

 2*653 to 2-654, and for crystals of quartz from Herkimer he cites 

 Penfield's determination as 2-66. 3 



All of these figures for quartz are higher than those for Arkansas 

 stone. So far, therefore, as specific gravity is concerned, Arkansas 



1 ' Ore Deposits,' 1884, p. 70. 



2 ' Whetstones and the Novaculites of Arkansas,' p. 93. 

 s ' System of Mineralogy,' 6th ed. 1892, p. 186. 



