-154 THE NATURAL HISTORY OF SELBORNE, 
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 archi- 
tectonic 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 
cradles 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. 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 inartificially laid together. 
Perseverance will accomplish anything; 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 the bank, 
and was of a different color from that which lay loose and 
bleached in the sun. 
In what space of time these little artists are able to mine 
and finish these cavities I have not been able to discover, for 
reasons given-above; but it would be a matter worthy of 
observation, where it falls in the way of any naturalist, to make 
his remarks. ‘This I have often taken notice of, that several 
holes of different depths are left unfinished at the end of 
summer. ‘To imagine that these beginnings were intentionally ~ 
made in order to be in the greater forwardness for next spring, 
is allowing, pérhaps, too much foresight and prudence in things 
to a simple bird. May not the cause of these hiding-places 
being left unfinished arise from their meeting in those places 
with strata too harsh, hard, and solid for their purpose, which 
