452 Dr. Mac Culloch on Ouart% Rock. 



on comparing these apparent interruptions with the actual causes 

 which produce them, that the fundamental evenness and direction 

 of the strata is no where altered, and that their discontinuities are 

 only the effects of partial elevations interfering with the visual line, 

 all the strata being straight and parallel to each other through 

 their whole extent. This line extends to the north north-west, and 

 the strata dip to the east north-east. In the Outlines of the mi- 

 neralogy of Jura, this angle is said to be 45°. It appeared to me 

 considerably less, but this sort of observation is not easily made, 

 except in favourable circumstances of position, and I was at no 

 pains to verify it accurately, considering it of no importance in a 

 case like this, whether the elevation were 10 or 12 degrees more 

 or less. It is only in cases where it is necessary to compare parti- 

 cular strata, either with the neighbouring ones or with each other, 

 that accuracy is required, and this accuracy is I fear much less fre- 

 quently attained than pretended to. These strata are generally 

 thin, often not exceeding six or eight feet in thickness, and I no 

 where observed that they were distorted or interrupted by veins of 

 any magnitude, or that they alternated with other rocks. It is true 

 that at an inaccessible part of the summit of the one on which I 

 stood, I observed a mass of dark-coloured rock, which the guide 

 informed me was a slaty stone. Future observers may find de- 

 tached specimens of it, and thus ascertain that which I attempted 

 in vain to investigate, but which the sequel of these remarks will 

 prove to be more than probable. 



Such is the appearance of the rocks as observed from the Paps of 

 Jura. In descending to the lower grounds, the stratified disposition 

 becomes more obscure, in consequence of the interruption to the 

 continuity of the rock from the thick covering of heather, and 

 from the irregular form of the surface which prevents a connected 



