170 Wild Life in a Southern County. 
The wall being old, some of the mortar had 
crumbled—it was not of the best quality—and here 
and there was a small cavity. These a portion of the 
birds tried to enlarge, while others boldly laboured in 
places where no such slight openings existed. It was. 
interesting to watch their patient efforts as they clung 
to the perpendicular wall like bats. Now, two or 
three flew off and described a few circles in the air, as. 
if to rest themselves, and then again returned to work. 
At last, convinced of the impossibility of penetrating 
the mortar, which was much harder beneath the 
surface, they went away in a body with a general 
twitter, leaving distinct marks of their shallow exca- 
vations. The circumstance was the more interesting 
because the road was much frequented (for a rural 
district) and many people stopped to look at them ; 
but the birds did not seem in the least alarmed, and 
evidently only left because they found the wall 
impenetrable. Instinct, infallible instinct, certainly 
would not direct these birds to such an unsuitable 
spot. Neither was there any peculiar advantage to 
attract them; it was not quiet or retired, but the 
reverse. The incident was clearly an experiment, 
and when they found it unsuccessful they desisted. 
If we suppose this flight of martins to represent 
a party emigrating from a sand quarry (there were 
three such quarries within a mile radius), where the 
population had overflowed, it seems possible to trace 
the motive which animated them. I imagine that the 
