340 Geographical Distrilmtion 



Madeira Islands (although not in either at the present period), 

 if the number of species of land shells be any criterion, have 

 not been since the origination of such species in the former. 

 "Wollaston {On the Variation of Species, p. 129) quotes it as the 

 opinion of Lyell that the Madeira beds in which fossil Helices 

 are found were deposited anterior to the destruction of the 

 "Atlantic Province," of which the Madeira Islands are sup- 

 posed to have been a part ; whereas the condition of the fauna 

 would lead to the supposition of its insular rather than conti- 

 nental origin. 



Wollaston, referring especially to three species of Helix found 

 in the Madeiras, says, " that these are actual species (saved 

 alive from their fellows, after the wholesale destructions in this 

 Atlantic province had been completed), and no results of 

 insular development, is demonstrated by the fact that two of 

 them (for the third has apparently become extinct*) have not 

 altered one iota since i\\e fussil jperiod.'''' From that and other 

 similar fiicts, he concludes, — first, that this quonda^n continent 

 was densely stocked at the beginning with foci of radiation 

 created expressly for itself; and, secondly, that the areas which 

 these various creatures had overspread, before the land of 

 passage was broken up, w^as extremely limited, — or, which 

 amounts to the same thing, that their emigratory progress was 

 unusually slow^ As regards the West Indies, the " quondam 

 continent" question does notarise, — there is no evidence of the 

 breaking up of " the land of passage." Not only are each of 

 tlie larger islands, according to Wollaston's views, " foci of 

 radiation," but as he states is the case in Madeira, so is it in 

 the West Indies, scarcely a gorge or woodland sierra exists 

 within their bounds " which does not harbor some species essen- 

 tially its own ; and in many instances the ranges of these crea- 

 tures are so local or confined, that they might be easily over- 

 looked in their respective neighborhoods." 



I admit to the fullest extent the slow migratory progress of 



* The species referred to, H. tiarella W. & B., has since been found alive. 



