170 ON BIO-GEOLOGY. [vn. 



of Machaon in the Cambridgeshire fens. I could talk 

 long about a similar phenomenon in the case of our 

 migratory and singing birds ; how many exquisite 

 species notably those two glorious songsters, the 

 Orphean Warbler and Hippolais, which delight our 

 ears everywhere on the other side of the Channel 

 follow our nightingales, blackcaps, and warblers 

 northward every spring almost to the Straits of 

 Dover, but dare not cross, simply because they have 

 been, as it were, created since the gulf was opened, 

 and have never learnt from their parents how to fly 

 over it. 



In the case of fishes, again, I might say much on 

 the curious fact that the Cyprinidse, or white fish 

 carp, etc. and their natural enemy, the pike, are 

 indigenous, I believe, only to the rivers, English or 

 continental, on the eastern side of the Straits of 

 Dover; while the rivers on the western side were 

 originally tenanted, like our Hampshire streams, as 

 now, almost entirely by trout, their only Cyprinoid 

 being the minnow if it, too, be not an interloper; 

 and I might ask you to consider the bearing of this 

 curious fact on the former junction of England and 

 France. 



But I have only time to point out to you a few 

 curious facts with regard to reptiles, which should be 

 specially interesting to a Hampshire bio-geologist. 

 You know, of course, that in Ireland there are no 

 reptiles, save the little common lizard, Lacerta agilis, 

 and a few frogs on the mountain-tops how they got 

 there I cannot conceive. And you will, of course, 

 guess, and rightly, that the reason of the absence of 

 reptiles is : that Ireland was parted off from England 



