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pained with looking, that I could no longer difcenr 
them. 
But, as my friend Klein feems to be fo pofitive, 
that the hirundo riparia, or fand martin, at the ap- 
proach of winter, retires into the holes, in which that 
fpecies breed up their young, and made their fummer’s 
refidence, and there pafs that cold feafon in a dor- 
mant ftate, as fnakes, lizards, and fome other ani- 
mals do, I have been the more follicitous to come at 
the truth. But as thefe fandy precipices, in which 
thefe martins build, are moftly inacceffible, fome 
years have palled, before I could find a fituation 
where the experiment could be fairly made, without 
difficulty or danger. Such a fand-hill I found in the 
parifh of Byfleet in Surry. The clergyman being my 
friend, and well qualified to make the experiment, 
at my requeft, was fo obliging to undertake it. I 
fhall give his letter to me, in his own words. 
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“ Dear Sir “ B y flce b Oflober 22, 1757. 
<{ I took a fquare of about twelve feet, over that 
part of the clift where the holes were thickeft, 
which, in going down from the furface, I judged 
would take in about forty holes. I fet to work,, 
and came to the holes; but found no martins, 
nothing but old nefts in the furtheft end of the 
holes, which were from a foot and half to two 
feet and half deep from the entrance. We care- 
fully fearched forty holes, but found no birds ; 
but at leaf! thirty of them had nefts. The paffage 
to them was very near in a ftraight horizontal line ; 
the neft was funk about an inch and half below 
the level of the paflage ; the materials next the 
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