Stutchburys Genus Cyprcecassis. 387 



and other philosophers eminent in optical science, that atten- 

 tion it is entitled to. 



My sight has been particularly good, having been able to 

 distinguish objects very clearly, near and at a great distance ; 

 and now, in my 69th year, I can distinguish a small speck of 

 mica, in a brown-red sandstone, at the distance of 4 yards ; 

 and, in the full bright light of the sun, the brilliant reflections 

 from facets of much smaller crystals of quartz. I was led to 

 this experiment by finding amongst our Scarborough gravel a 

 brown-red sandstone pebble, the crystals of which brilliantly 

 reflected the full light of the sun. Viewing it in the house, 

 on a table before my window, with my spectacles on, and the 

 addition of a small pocket lens, the glistening specks appeared 

 too small for me to decide whether they consisted of quartz or 

 mica ; but, as I had lately selected from the same gravel spe- 

 cimens of mica slate, and mica sandstones, of all degrees of 

 fineness, it occurred to me that small specks of mica were 

 always visible without the sun's full bright light. I found 

 them so; and, by collating the sandstone with the finest 

 grained micaceous specimen, both on one piece of paper, 

 shifted alternately into the bright and shady light of the sun, 

 we have a clear and ready distinction between the finest grains 

 of mica and quartz, without the aid of glasses, and that even 

 at the distance of 4 yards. 



In my practical observations on the different kinds of land, 

 1 had long observed, by the glistening in footpaths, how we 

 may readily distinguish the finest sand in soil ; and, at Harro- 

 gate, I have often amused myself, on the nicely sanded foot- 

 paths about the Swan Hotel, by fixing my eye upon any 

 detached crystal (of mill-stone grit) which brilliantly reflected 

 the light of the sun, and not without speculating on the ap- 

 plication of such brilliant reflections to some useful purpose : 

 but, in geology, the brilliancy of those facets of quartz crystals 

 in our coarsest sandstone seems to render doubtful the 

 " theory of sandstones being derivative rocks." — William 

 Smith, LL.D. Scarborough, May 10. 1827. 



Objection to Mr. Stutchbury's Genus Cyprcecassis (p. 214. 

 — The absence of varices is not a character sufficiently dis- 

 tinctive to form a genus, since the Nassa incrassata of Fleming, 

 though usually without, sometimes assumes varices, and puts 

 on the appearance of a miniature Triton. I have also in my 

 collection more than one Triton without varices. As to the 

 natural polish of those shells without varices enumerated as 

 species of the proposed genus, and, as said, occasioned from 

 their being covered by the lobes of their mantle, I should be 

 glad to learn what else occasions the superior polish of Cassis 



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