INTRODUCTORY CHAPTER. lxxv 



limestone was deposited ; but its higher peaks were still above water, and 

 formed an island, peopled mainly by African species— the plants being the 

 fragmentary remains of the old African flora — but with an admixture of 

 eastern and other Asian forms. Thereafter it gradually rose, undergoing 

 violent volcanic disturbance, and again became part of the mainland, though it 

 is likely for only a short period, and during this union the life of the adjacent 

 continent covered its plains and filled its valleys. Subsequently it reverted to 

 its insular condition, in which state it has remained. 



An island certainly from tertiary times, the various denuding agents have 

 during the interval continued to sculpture the surface of Socotra, and have 

 brought about the quaint outline we see at the present day ; but as a land- 

 surface it dates from a far greater antiquity, back indeed to the permian epoch ; 

 and the species which now people its surface exhibit peculiarities which bear 

 alike the stamp of their ancient origin and the imprint of the isolation to which 

 they have been subjected. 



