92 EVOLUTION [CHAP. II 



Letter 47 of the period required to convert a swan into a goose, or vice 

 versa. Nine feet did the Rimutaka chain of New Zealand 

 gain in height in Jan., 1855, and a great earthquake has 

 occurred in New Zealand every seven years for half a century 

 nearly. The Washingtonia (California!! conifer) l lately ex- 

 hibited was four thousand years old, so that one individual 

 might see a chain of hills rise, and rise with it, much [more] 

 a species and those islands which J. Hooker describes as 

 covered with New Zealand plants three hundred (?) miles to the 

 N.E. (?) of New Zealand may have been separated from the 

 mainland two or three or four generations of Washingtonia 



ago. 



If the identity of the land-shells of all the hundreds of 

 British Isles be owing to their having been united since the 

 Glacial period, and the discordance, almost total, of the shells 

 of Porto Santo and Madeira be owing to their having been 

 separated [during] all the newer and possibly older Pliocene 

 periods, then it gives us a conception of time which will aid 

 you much in your conversion of species, if immensity of time 

 will do all you require ; for the Glacial period is thus shown, 

 as we might have anticipated, to be contemptible in duration 

 or in distance from us, as compared to the older Pliocene, 

 let alone the Miocene, when our contemporary species were, 

 though in a minority, already beginning to flourish. 



The littoral shells, according to MacAndrew, imply that 

 Madeira and the Canaries were once joined to the mainland 

 of Europe or Africa, but that those isles were disjoined so 

 long ago that most of the species came in since. In short, 

 the marine shells tell the same story as the land shells. Why 

 do the plants of Porto Santo and Madeira agree so nearly ? 

 And why do the shells which are the same as European or 

 African species remain quite unaltered, like the Crag species, 

 which returned unchanged to the British seas after being 

 expelled from them by glacial cold, when two millions (?) of 

 years had elapsed, and after such migration to milder seas ? 

 Be so good as to explain all this in your next letter. 



1 Washingtonia, or Wellingtonia, better known as Sequoia. Asa 

 Gray, writing in 1872, states his belief that "no Sequoia now alive can 

 sensibly antedate the Christian era" (Scientific Papers, II., p. 144). 





