22 



Mediterranean having been formerly divided 

 into several separate basins, of which Sicily and 

 the Isle of Crete appear to mark the ancient 

 limits. We will not here risk the solution of 

 these problems, but will satisfy ourselves in fix- 

 ing the attention on the striking contrast in the 

 configuration of the land in the eastern and west- 

 ern extremities of Europe. Between the Baltic 

 and the Black Sea, the ground is at present 

 scarcely fifty toises above the level of the ocean, 

 while the plain of La Mancha, if placed between 

 the sources of the Niemen and the Borysthenes, 

 would figure as a group of mountains of consi- 

 derable height. If the causes, which may have 

 changed the surface of our planet, be an inte- 

 resting speculation, investigations of the pheno- 

 mena, such as they offer themselves to the mea- 

 sures and observations of the naturalist, lead to 

 far greater certainty. 



From Astorga to Corunna, especially from 

 Lugo, the mountains rise gradually. The se- 

 condary formations gently disappear, and are 

 succeeded by the transition rocks, which indi- 

 cate the proximity of primitive strata. We found 

 considerable mountains composed of that anci- 

 ent gray stone, which the mineralogists of the 

 school of Fribourg name grauwakke, and grau- 

 waJckefischiefer. I do not know whether this for- 

 mation, which is not frequent in the south of 

 Europe, has hitherto been discovered in other 



