6 ST. JAGO CAPE DE VERD ISLANDS. [chap. i. 



some miles along the coast, and at the height of about forty-five 

 feet above the water. Upon examination, this white stratum is 

 found to consist of calcareous matter, with numerous shells em- 

 bedded, most or all of which now exist on the neighbouring 

 coast. It rests on ancient volcanic rocks, and has been covered 

 by a stream of basalt, which must have entered the sea when the 

 white shelly bed was lying at the bottom. It is interesting to 

 trace the changes, produced by the heat of the overlying lava, on 

 the friable mass, which in parts has been converted into a crys- 

 talline limestone, and in other parts into a compact spotted stone. 

 Where the lime has been caught up by the scoriaceous fragments 

 of the lower surface of the stream, it is converted into groups of 

 beautifully radiated 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 be- 

 lieve, 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 dis- 

 tinguished on the coast, forming lines of cliffs of less height, but 

 stretching 1 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 branchiae or 

 lungs. It feeds on the delicate sea-weeds which grow among 

 the stones in muddv and shallow water ; and I found in its sto- 

 mach 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 



