THE AVES ISLANDS. 



185 



and a few low shrabby bushes, in addition to sedums, 

 grasses (Carex) and a salt-loving plant of a sprawling 

 habit and with a salty juice (probably a species of 

 samphire or salicornia). Fish abound among the reefs, 

 which are also frequented by turtle, while the rest of the 

 natural population is made up of boobies (S. leucogastra) 

 flamingoes, herons (Ludwig saw four different species), 

 curlews, yellow -shanks, plovers, turnstones and other 

 shore birds. 



The Los Roques group also consists of a mass of 

 flat coral islets which occupy a space of fourteen miles 

 in a north and south direction, and twenty-four from east 

 to west. The description, which we have just given, of the 

 Aves islands would apply ahnost equally well to this 

 group, except that in the northern extremity of the group 

 there is an islet called El Roque, which rises to a height 

 of several hundred feet, and is visible as a high cone- 

 shaped mass at a good distance out at sea. On one of 

 our cruises we passed it at a distance of about ten miles, 

 and as the other low cays were invisible from so far away, 

 the effect of this pyramid of rock, rising lone and grey 

 from the sea, was very strange. This high rocky islet 

 differs from all the rest of the groups in consisting, as far 

 as one can understand Ludwig's description (loc. cit.), 

 of a medley of various forms of Archaean schists and rocks 

 which trend in a south-west to north-easterly direction. 

 On the east and south sides are found some crystalline 

 Archaean limestones, while the main mass contains 

 varieties of granite such as biotite and diorite, and in 

 addition he found augite and greenstone-schists. 



Hence one may conclude that both these groups of 

 islands have been simply formed by coral reefs w^hich have 

 grown upwards to the surface from a submarine plateau 

 of Archaean rocks. 



With the exception of the island of El Roque, which 

 probably has resulted from some more violent upthrust as 

 the consequence of vast pressure beneath, we may look 

 upon both groups of islands as representing a stage of 



