with Geognostical Observations, Qc. 185 



disorder is exhibited. We soon discover the cause of these 

 derangements. Scarcely has the limestone with gryphites be- 

 gun in the lower beds to mix itself with sand, and to change 

 into sandstone, when we see it elevated and torn at several 

 points by black and red lavas, and by compact trachytic masses. 

 We descended in zig-zag the almost perpendicular declivity of 

 this mountain ; and when we arrived below, we saw to the bot- 

 tom of a precipice, or of a crevice, on the banks of the Ourda, 

 which falls impetuously from rock to rock. Here we discover 

 heaved up strata of argillaceous schistus. 



The lavas which are thus found at the limit of the sand- 

 stone and of the argillaceous schistus are mostly of a black 

 colour, filled with vesides greatly elongated in one direction, 

 and lying parallel to one another, so that these lavas seem to 

 have suffered a great pressure by the superposed beds in tra- 

 versing them. These vesicles are entirely empty ; and with 

 the exception of some white points nearly microscopic, we can- 

 not discover any trace of the substances which so often fill the 

 cavities of other lavas. Sometimes small crystals of amphibole 

 are enveloped in their paste. At other places the cavities arc- 

 very rare and very small. The mass becomes highly compact, 

 takes a gray colour, mixed with small spots of a pale red, 

 cleaves into thin lamina;, and presents in general the mineralo- 

 gical characters of a trachytic paste : The crystals of glassy 

 feldspar are, however, wanting ; and we discover here and there 

 small brilliant points of mica of a bronze colour. 



The argillaceous schistus alternates in some places with a 

 species of psammite, (grauwacke,) which is, however, distin- 

 guished from the common grauwacke by its white colour. The 

 strata of this rock are very much inclined; on the banks of the 

 river Kinjal, which we descended on the same day, the beds 

 of argillaceous schistus present so many irregularities in their 

 arrangement, that it is easy to observe die effect of a general 

 derangement occasioned by the eruption of trachytic masses, 

 which, as we shall presently see, penetrate every where the 

 soil of the argillaceous schistus. 



The interval between the last sandstone which I have men- 

 tioned and the argillaceous schistus, is occupied with a parti- 

 cular Coronation of grts lumiMw. This I particularly obiery,- 



