A MOUNTAIN TARN. 169 



result of a special creation, we could have 

 had no alternative but to suppose that each 

 of these kinds of mountain trout was specially 

 created in and for the particular little pool 

 where we now find it. But the new theory 

 of evolution simply teaches us that each trout 

 has been evolved under peculiar circum- 

 stances to suit the special conditions of these 

 isolated sheets of water in which they live. 

 Let us look a little closely at the position of 

 Llyn Gwernant, and consider why a unique 

 kind of trout should have been evolved just 

 there rather than elsewhere. 



The tarn itself, one can see at a glance, 

 must be a glacial hollow. It was scooped 

 out by the grinding action of ice in the last 

 glacial epoch. Look up the glen, and then 

 down, and you will see that in either direction 

 the valley widens out from the lake as a 

 centre. But just about the neighbourhood 

 of the lake itself the sides trend inwards, so 

 as to enclose a small pass or gorge ; and 

 when the whole combe formed the bed of an 



