384 ORIGIN OF LIFE IN AMERICA 



to Africa, whereas I favour the theory that such a connec- 

 tion could only have persisted indirectly by way of the Antilles 

 and southern Europe. 



It has been urged that if a land bridge had once existed 

 between Brazil and west Africa we ought to find some traces 

 of sedimentary rocks on the few islands that are scattered 

 about in the intermediate area, like Fernando de Noronha, St. 

 Paul's, St. Helena, Ascension and Tristan da Cunha, whereas 

 all these are believed to be composed of volcanic rocks. Pro- 

 fessor Schwarz,* nevertheless, affirms thafc although Ascen- 

 sion consists of volcanic rock the substratum is granitic. St. 

 Paul's island, he thinks, is mainly metamorphic in structure, 

 and there are signs of its having been subjected to considerable 

 earth movements. Continental types of rocks occur on Tristan 

 da Cunha. Consequently Professor Schwarz concludes that 

 these Atlantic islands furnish some geological testimony for 

 the belief in a Mesozoic Continent in the position of the 

 southern Atlantic lasting until the beginning of the Tertiary 

 Era. 



The island of Fernando de Noronha lies about two hundred 

 miles east of Cape San Roque on the coast of Brazil. Since 

 its discovery in 1503 both the original fauna and flora of the 

 island have been laid waste by early settlers, so that only 

 vestiges of these are left. The splendid trees that once clothed 

 the island are gone and with them probably the greater part 

 of the fauna. A mammal, at any rate, existed on Fernando de 

 Noronha when it was discovered, but it has quite vanished. 

 Mr. Ridley, who visited Fernando de Noronha in 1887, noticed 

 that quite a number of species of animals and plants had evi- 

 dently been introduced by human agency. Many others, he 

 thinks, have been transported to the island from the main- 

 land by winds, although he noted that the smaller birds and 

 a large proportion of the smaller insects are endemic. A few, 

 he remarks, may possibly have been brought over on the feet 

 of wading birds. There still remains a small group of indi- 

 genous species which are difficult to account for, on the hypo- 

 thesis of accidental distribution. The subterranean lizard 



* Schwarz, E. H. L., "Land-connection between Africa and ruth 

 America," pp. 81 90. 



