6 ST. JAGO CAPE DE VERD tSLAKDS. [CHAP. i. 



fibres resembling arragonite. The beds of lava rise in successive 

 gently-sloping plains, towards the interior, whence the deluges of 

 melted stone have originally proceeded. Within historical times, 

 no signs of volcanic activity have, I believe, been manifested in any 

 part of St. Jago. Even the form of a crater can but rarely be 

 discovered on the summits of the many red cindery hills ; yet the 

 more recent streams can be distinguished on the coast, forming 

 lines of cliffs of less height, but stretching out in advance of those 

 belonging to an older series : the height of the cliffs thus affording 

 a rude measure of the age of the streams. 



During our stay, I observed the habits of some marine animals. 

 A large Aplysia is very common. This sea-slug is about five inches 

 long ; and is of a dirty yellowish colour, veined with purple. On 

 each side of the lower surface, or foot, there is a broad membrane, 

 which appears sometimes to act as a ventilator, in causing a current 

 of water to flow over the dorsal branchia) or lungs. It feeds on the 

 delicate sea-weeds which grow among the stones in muddy and 

 shallow water ; and I found in its stomach several small pebbles, as 

 in the gizzard of a bird. This slug, when disturbed, emits a very 

 fine purplish-red fluid, which stains the water for the space of a 

 foot around. Besides this means of defence, an acrid secretion, 

 which is spread over its body, causes a sharp, stinging sensation, 

 similar to that produced by the Physalia, or Portuguese man-of- 

 war. 



I was much interested, on several occasions, by watching the 

 habits of an Octopus, or cuttle-fish. Although common in the 

 pools of water left by the retiring tide, these animals were not 

 easily caught. By means of their long arms and suckers, they 

 could drag their bodies into very narrow crevices ; and when thus 

 fixed, it required great force to remove them. At other times they 

 darted tail first, with the rapidity of an arrow, from one side of the 

 pool to the other, at the same instant discolouring the water with 

 a dark chestnut-brown ink. These animals also escape detection 

 by a very extraordinary, chameleon-like power of changing their 

 colour. They appear to vary their tints according to the nature of 

 the ground over which they pass : when in deep water, their general 

 shade was brownish purple, but when placed on the land, or in 

 shallow water, this dark tint changed into one of a yellowish green. 

 The colour, examined more carefully, was a French grey, with 

 numerous minute spots of bright yellow : the former of these varied 



