Nature of Mineral Veins. 64>5 



insect Hylesinus Scolytus, and says, on the authority of a 

 Mr. Lee, "Distruit ulmos Angliae." Gyllenhall (Insecta 

 Suecica, torn. iii. 34?6, 347.) calls it Eccoptogaster Scolytus 

 (sxxo7ttcjo ya<rTY}p, excido et venter) ; and says, ** Habitat in 

 truncis exsiccatis Betulse albae sub cortice, passim ; " and it is 

 somewhat singular that, in his descriptions of the various 

 insects of this genus, he does not specify one as feeding on 

 the elm: he does, however, mention dead trees (arborum 

 mortuarum) as the habitat of several. No other tree, that I 

 have observed, but the elm, has been injured by this insect, 

 in our neighbourhood. — O. Clapton^ Oct. 15. 1836. 



Nature of Mineral Veins. — Reading over the interesting 

 lecture on the mineralogy and geology of Nova Scotia, in the 

 last Number of your Magazine, I noticed a remark (p. 579.), 

 that " the minerals which occasionally fill up veins and 

 cavities in rocks are always component parts of the rocks in 

 which they are found." It is difficult to find a rule altoge- 

 ther without exceptions ; and exceptions to this rule must 

 always be difficult to account for: yet they exist. It is a 

 well-known fact, that veins of compact quartz rock, and 

 cavities containing quartz crystallised, are frequent in 

 granites ; the cavities, however, being generally in the quartz 

 veins, rarely in that granite which contains them, except in 

 the form of mere fissures. Flexible amianthus, green and 

 white, with large crystals of felspar, chlorite, and schorl, is 

 usually found accompanying the quartz; and, with these, it is 

 a thing of not very unfrequent occurrence to meet with crys- 

 tals of calcareous spar, neither small nor few in number. 

 There would be little singularity in this, if the cavities had 

 ever been exposed to the air, or to the action of water by 

 infiltration ; but, when it is considered that they are in the 

 heart of the granite or quartz, if not far from its surface, at 

 least entirely secured from the influence of extraneous cir- 

 cumstances, and only to be discovered by the indefatigable 

 search of the crystal-hunter, the circumstance becomes re- 

 markable, if not unaccountable. 



Mineral veins are, indeed, formed, not only in compound 

 rocks from their component parts, but also in simple rocks 

 from their constituent parts. Thus zeolites occur in trap 

 (by the by, at, p. 580., has not the word "steatites" been 

 accidentally substituted, or taken down erroneously, for 

 "zeolites?" I do not know what is meant by "opaque 

 limespar :" but steatite does not radiate in its crystallisation ; 

 and, when found in floetz trap, it is usually in angular frag- 

 ments) ; and thus quartz veins and crystals of chiastolite are 

 formed in clay slate, the one from its silex, the other from its 



