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Cn. XLI.] INSULAR FLOEAS AND FAUNAS CONSIDERED. 



40'' 



* 



far from land and surrounded by a deep ocean, we find that 

 they are remarkable for the number of peculiar species of 

 animals and plants which they contain^ even a single island of 



L 



many 



exclusively belonging to it. Yet even in such localities an 

 affinity can be traced between the insular forms considered 

 as a Avliole, and those of the nearest continent — a relationship 

 exceeding that which connects them with the fauna and flora 

 of more distant parts of the globe. 



shall refer chiefly to 



/ 



I 



Madeiras 



oceanic archipelagos, as I have mj 



visited them and 



studied their geological structure, without a knowledge of 

 which the speculations and theories of a zoologist or botanist 



e mode 

 must n 



For in the first 



water durinp- 



place we require information as to the period of the past to 

 which the origin of the islands can be traced back, and then we 

 have still to enquire whether they are fragments of a pre- 

 existing continent, or were formed in mid-ocean by volcanic 

 eruptions. 



If we find evidence that in the case of the Atlantic 

 islands the latter conclusion is true, we have still to learn 

 whether each of them has continued above 

 the whole course of its growth by successive eruptions, or 

 whether it may have undergone oscillations of level, by alter- 

 nate upheaval and subsidence. To 



we are fortunately able to give a satisfactory answer. It 

 maybe afiirmed that the earliest eruptions took place in that 

 part of the Middle Tertiary period which I have called Upper 

 Miocene. As soon as the first solid lavas raised their heads 

 above water, they were exposed to the action of the waves, 

 and fragments of volcanic rocks were detached and rounded 

 on the shore, and some of them swept into the adjoining 



most 



form 



glomerates, or sands and sandstones, in which corals and 



By far the larger 



Miocene 



number of these species are now extinct. Their fossil re- 

 mains have been rendered visible to us by their having been 



D D 2 



