118 Dr. Berger oh the physical Structure 



N. to S. which is the same with the course of the river flowing 

 through it. Thus it appears that these vallies, which are all similar 

 to each other, are perpendicular to the mountain plain.* 



Leaving the bed of the river Erme to the left, about five minutes 

 walk from Ivy-Bridge, we pass some farm houses at the bottom of 

 a small detached hill, the name of which I did not learn, nor do I 

 find it laid down in the common maps of the county : it is situated 

 N.N.E. of Ivy-Bridge, and from thence to the top of the hill is about 

 two miles and a half by the nearest road. This small hill, the only 

 abrupt face of which is towards the south, is situated on the ex- 

 terior line of the mountains of Dartmoor, on the first plain they form 

 from the sea coast. The upper half is composed of a rock which 

 I call a porphyritic granite,'f and the lower part as well as the base 

 is of grauwacke. I found the summit to be one thousand one 

 hundred and thirty feet above the level of the sea, and the greatest 

 height to which the grauwacke rises on its sides is six hundred and 

 thirty-one feet. 



There is on the right bank of the Erme another small hill, facing 

 the latter, equally rounded in its outline : both have that appearance 

 which Saussure calls moutonnee^ an expression in my opinion pecu- 

 liarly applicable to the low granite mountains of the ci-devant Forez. 



* In the Alps, the vallies arc longitudinal and trajisveise ; in Jura, thcj are almost 

 all longitudinal ; in the Vosges, the greater part arc oblique ; in the Pyrenees, they are 

 nearly at right angles. Journal des Mines, IVo. 126, 



+ The base of this porphyritic granite is a beautiful kind of felspar of a brick-red 

 colour, confusedly crystallized, in which arc imbedded crystals of vitreous quartz, horn- 

 blende and tender steatite of a greenish yellow. 1 found on the summit several adven- 

 titious blocks of amethystine quartz. 



X The mountains which Saussure designates by this expression (moutonnee) are com- 

 posed of an assemblage of rounded tops, covered sometimes with wood, but more fre- 



