108 
NATURAL HISTORY 
abounding, but near vast pools or rivers ; and in particular 
it has been remarked that they swarm in the banks of the 
Thames in some places below London bridge. 
It is curious to observe with what different degrees of 
architectonic skill Providence has endowed birds of the same 
genus^ and so nearly correspondent in their general mode 
of life ! for while the swallow and the house martin discover 
the greatest address in raising and securely fixing crusts or 
shells of loam as cunahula for their young, the bank martin 
terebrates a round and regular hole in the sand or earth, 
which is serpentine, horizontal, and about two feet deep. 
SAND martins' colony AT OAKHANGER. 
At the inner end of this burrow does this bird deposit, in a 
good degree of safety, her rude nest, consisting of fine 
grasses and feathers, usually goose feathers, very inartifi- 
cially laid together. 
Perseverance will accomplish any thing : though at first 
one would be disinclined to believe that this weak bird, with 
her soft and tender bill and claws, should ever be able to 
bore the stubborn sand bank without entirely disabling 
herself ; yet with these feeble instruments have I seen a pair 
of them make great dispatch ; and could remark how much 
they had scooped that day by the fresh sand which ran down 
