chap. i. Ancient Volcanic Hills. 2 1 



always in one direction (as at the Cape de Verde Archi- 

 pelago), the effects of atmospheric degradation are pro- 

 bably much greater than would at first be expected ; 

 for soil in this case accumulates only in a few protected 

 hollows, and being blown in one direction, it is always 

 travelling towards the sea in the form of the finest dust, 

 leaving the surface of the rocks bare, and exposed to 

 the full effects of renewed meteoric action. 



Inland hills of more ancient volcanic rocks. — These 

 hills are laid down by eye, and marked as A, B, C, &c, 

 in the woodcut-map. They are related in mineralogical 

 composition, and are probably directly continuous with 

 the lowest rocks exposed on the coast. These hills, 

 viewed from a distance, appear as if they had once 

 formed part of an irregular table-land, and from their 

 corresponding structure and composition this probably 

 has been the case. They have fiat, slightly inclined 

 summits, and are, on an average, about 600 feet in 

 height ; they present their steepest slope towards the 

 interior of the island, from which point they radiate 

 outwards, and are separated from each other by broad 

 and deep valleys, through which the great streams of 

 lava, forming the coast-plains, have descended. Their 

 inner and steeper escarpments are ranged in an ir- 

 regular curve, which rudely follows the line of the shore, 

 two or three miles inland from it. I ascended a few of 

 these hills, and from others, which I was able to examine 

 with a telescope, I obtained specimens, through the 

 kindness of Mr. Kent, the assistant-surgeon of the 

 1 Beagle '; although by these means I am acquainted with 

 only apart of the range, five or six miles in length, yet 

 I scarcely hesitate, from their uniform structure, to 

 affirm that they are parts of one great formation, stretch- 

 ing round much of the circumference of the island. 



The upper and lower strata of these hills differ 



