SOME GENERAL OBSERVATIONS ON THE WHOLE QUATERNARY. 599 



peculiar to Africa and Madagascar, and are probably indigenous ; the 

 animals of the latter group are similar to the Pliocene animals of Eu- 

 rasia, and are probably invaders. The explanation is as follows: 

 During late Tertiary times, Africa was separated from Eurasia prob- 

 ably by a sea, and inhabited only by the group which we called in- 

 digenes. Then came the Glacial oscillations, which opened a gateway 

 into Africa, and the concomitant climatic changes which drove the 

 Eurasian Pliocene animals southward. These invaders soon domi- 

 nated the weaker indigenes and were subsequently isolated in their 

 new home. The struggle which followed has produced considerable 

 change in both groups, but especially in the indigenes. 



3. Madagascar. — The mammalian fauna of Madagascar is very re- 

 markable ; nearly all the species being peculiar to that island. There 

 is, however, a general resemblance to the indigenes of Africa. The 

 explanation is as follows : During Tertiary times, Madagascar was a 

 part of the African Continent, and both inhabited by the same animals, 

 viz., the indigenes. But in Pliocene times, before the northern inva- 

 sion, it was separated, and therefore the invasion did not reach it. 

 Meanwhile by long isolation, the Malagasian fauna changed slowly to 

 its present state, but the change was not so great as in their African 

 congeners, who had to bear the brunt of the struggle with invaders. 

 Therefore, we have in the Malagasian fauna a somewhat nearer ap- 

 proach to the Tertiary fauna of both. 



4. British Isles. — The fauna and flora of the British Isles are almost 

 but not quite identical with those of Europe. Between the two there 

 are strong varietal but not specific differences. They are also some- 

 what less rich, some species being wanting which are found on the 

 continent. This is especially true of Ireland. The explanation is as 

 folloAvs : The climatic changes of the Glacial epoch, and especially the 

 submergence of the Champlain (Fig. 942) completely destroyed the 

 indigenous species of these islands. But, during the Terrace, they 

 were again broadly connected with the continent, and therefore colo- 

 nized by continental species. They have been again separated, and 

 divergence of organic forms has again commenced ; but the period of 

 connection was so brief that the colonization, especially in the extreme 

 parts, was not completed before re-isolation ; and the time since re- 

 isolation has been too short for the divergence to go very far ; it has 

 reached only varietal differences. 



5. Coast Islands of California. — Along the coast of the southern 

 part of California there is a string of bold, rocky islands, two thousand 

 feet high, and about fifty miles off shore. The flora of these islands, 

 as shown by Prof. Greene,* is very remarkable. Of nearly three 



* Bulletin of the California Academy of Sciences, No. 7. 



