60 KOCK OF GIBRALTAE. ch. hi, 



explain the fact that a particular species is limited to a 

 very small district. These considerations do not, however, 

 fully explain the known facts regarding some regions of 

 the earth possessing an exceptional number of peculiar 

 species confined to small areas, the most remarkable of 

 which are Asia Minor, South Africa, South-western Aus- 

 tralia, and that which we are now discussing; and in 

 weighing the evidence afforded by the floras of the oppo- 

 site coasts as bearing on the probable duration of such a 

 barrier as the Strait of Gibraltar, it is best to leave out of 

 account all species that are not known to be widely dis- 

 tributed. Here our very limited knowledge of the flora of 

 North Marocco opposes a considerable difficulty. Subject 

 to such light as future observation will throw upon the 

 subject, it may be said that, so far as mere botanical evi- 

 dence goes, we should infer that the barrier was not present 

 at the time when the great majority of the existing plants 

 spread into this region ; but that it has been established 

 long enough to oppose a limit to the further difi"usion of 

 many species that qtherwise would, in all probability, be 

 found on both sides of the Strait, thus indicating a period 

 geologically recent, but very ancient as compared with the 

 historic record. 



On the following morning we crossed the bay to Gib- 

 raltar, and, still finding no means of conveyance to Tangier, 

 endeavoured to console ourselves by botanising on the 

 ' Eock.' Later in the day the impatience natural to the 

 British traveller induced us to open negotiations for the 

 hire of one of the numerous tug steamers that make hand- 

 some profits by helping becalmed ships through the Strait. 

 The first demand of one hundred dollars helped to moderate 

 our ardour ; and, though the more reasonable sum of forty- 

 five dollars was afterwards named by another merchant, we 

 finally decided to remain a second night in Europe, and 

 await the ordinary steamer on the following day. 



It is well known that all the rules which prevent 

 unauthorised persons from prying into the arcana of a 



