18441858] EDWARD FORBES 53 



date of the letter is fixed by Forbes's lecture given at the Royal Insti- 

 tution on Feb. 27th, 1846 (according to L. Horner's privately printed 

 Memoirs, II. , p. 94). 



Wednesday. 3, Southwark Street, Hyde Park. [1846.] Letter 20 



Dear Darwin 



To answer your very welcome letter, so far from being 

 a waste of time, is a gain, for it obliges me to make myself 

 clear and understood on matters which I have evidently put 

 forward imperfectly and with obscurity. I have devoted the 

 whole of this week to working and writing out the flora 

 question, for I now feel strong enough to give my promised 

 evening lecture on it at the Royal Institution on Friday, and, 

 moreover, wish to get it in printable form for the Reports of 

 our Survey. Therefore at no time can I receive or answer 

 objections with more benefit than now. From the hurry 

 and pressure which unfortunately attend all my movements 

 and doings I rarely have time to spare, in preparing for 

 publication, to do more than give brief and unsatisfactory 

 abstracts, which I fear are often extremely obscure. 



Now for your objections which have sprung out of my 

 own obscurities. 



I do not argue in a circle about the Irish case, but treat 

 the botanical evidence of connection and the 'geological as 

 distinct. The former only I urged at Cambridge ; the latter 

 I have not yet publicly maintained. 



My Cambridge argument 1 was this: That no known currents, 

 whether of water or air, or ordinary means of transport, 2 would 



the Existing Fauna and Flora of the British Isles and the Geological 

 Changes which have affected their area" (Mem. Geol. Surv., Vol. I., 

 p. 336, 1846). (See Proc. Roy. Soc., Vol. VII., p. 263, 1856; Quart. 

 Journ. Geol. Soc., Vol. XL, p. xxvii, 1855 ; and Ann. Mag. Nat. Hist., 

 Vol. XV., 1855.) 



1 "On the Distribution of Endemic Plants," by E. Forbes, Brit. Assoc. 

 Rep., 1845 (Cambridge), p. 67. 



2 Darwin's note on transportation (found with Forbes' letter): "Forbes' 

 arguments, from several Spanish plants in Ireland not being transported, 

 not sound, because sea-currents and air ditto and migration of birds in 

 same lines. I have thought not-transportation the greatest difficulty. 

 Now we see how many seeds every plant and tree requires to be regularly 

 propagated in its own country, for we cannot think the great number of 

 seeds superfluous, and therefore how small is the chance of here and 

 there a solitary seedling being preserved in a well stocked country." 



