S5S 
the Original Form of the Pyrenees. 
lowest protuberances ; and that, lastly, immediately after this 
revolution, the ridge of the primitive formation was, without 
doubt, at the same time that of the whole chain of the Pyrenees, 
Now, as we observe at the present day, that the lidge of the 
Pyrenees, with the exception ol a small number of places, is no 
longer the ridge of the granitic chain, which is found removed 
at some distance to the north ; but that this geographic ridge is 
composed of more modern rocks, which generally surpass the 
primitive formation in height, we are naturally led to presume 
that the Pyrenees have undergone a second very considerable 
degradation. 
The disposition of the rocks, and the external form of the 
mountains, appear to determine the period of this revolution. 
It is probable that it has taken place after the formation of the 
transition deposite, and before the excavation of the presently ex- 
isting valleys, and consequently before the deposition ol the 
trap formation, which, as we shall see in the sequel, appears to 
be of a very late origin. 
Observation tends to induce a presumption, that this degra* 
dation has principally attacked the ridge then existing, and all 
the northern aspect of the chain. 
\V e shall represent by a diagram the results which have given 
rise to this supposition. 
Fig. 9. PI. IX., represents the vertical and transverse section 
ABC of the Pvrenees in the direction of their breadth, such as 
we presume it to have been before these mountains underwent 
the degradation of which we have been speaking. We see in 
this section the two declivities AB and AD of equal size ; the 
granite occupying the centre, and forming the ridge of the chain ; 
the transition formation, and the secondary formation, distribu- 
ted in nearly equal quantities, upon the south and north sides, 
resting upon the granite. 
Let us now suppose that all the portion of these mountains 
situated between A, B, and C, has been destroyed by the effect of 
some power acting from north to south, in such a manner that 
there remains only the part situated between C, B, and D. 
The necessary consequence of this degradation would be a 
considerable change in the external form of the whole chain of 
VOL. XI. NO. 22. OCT. 1824 2 
