380 0N TIIE M.EONAST ftUBY. 



Valmahargucs, 6 kil. [8 J miles] north of Montpelliei 1 ; 

 and likewise in a stratum of basaltic tufa 3 kil. [15 fur- 

 longs] long, at the bottom of a hill called lou Hdout, or 

 lou Ndont, near Prades, on the north-east of Mont- 

 fcrrier. 

 Is tbe pleonast A question, by no means uninteresting, that naturally 

 Suction? Pr ° P rescn * s itself, is, whether the pleonast ruby be a volcanic 

 product, or not. From its hardness it might be presumed, 

 that it is altogether foreign to the lavas, and formed in the 

 humid way, anterior to its deposition in the strata where it 

 Probably it be- is found. It may be said, that none has yet been seen in 

 JSKSkb**" the Iaya of the Vivarais, Auvergne, Etna, the Lipari 

 islands, Iceland, or the Isle of France; but only in the 

 cavities of some rocks of Vesuvius, Somma, Closterlach, 

 and Campania. Hence we have sufficient reason to, believe, 

 that it belongs to the primitive rocks, and that to see it in- 

 timately united with the tourmalines of Ceylon is sufficient 

 though sup- to convince us of this. Brongniart however is of opinion, 



fobe o/thele- tnat tn ' s m ^ nera '' as we ^ as the telesia, or corundum, be- 

 condary forma- longs to the secondary trap formation. His opinion is 

 ll0ru founded perhaps upon that of Werner; who judges from 



the nature of the strata, of which the sand containing co- 

 rundums appears to be the remains, that those of a hard- 

 ness much superior to the pleonast must belong to that for- 

 mation. Thus as basaltes and basaltic tufa are rocks of the 

 secondary trap mountains, and these are met with in the 

 places where the pleonast is found, this opinion appears to 

 have some probability : but as we have not yet any accurate 

 description of the mineralogic'al situation of the corun- 

 dums; and as the adamantine spar is found in granite rocks, 

 entering even into their composition in the same manner as 

 feldspar; we may consider the corundum, adamantine spar, 

 and pleonast as belonging exclusively to the primitive for- 

 mations. This opinion however can rank only as a proba- 

 bility, till we have a precise knowledge of the miheralo- 

 gical situation of these interesting substances. 



VIII. On 



