VOL. LI.] PHILOSOPHICAL TRANSACTIONS. 42/ 



martin, at the approach of winter, retires into the holes, in which that species 

 breed up their young, and made their summer's residence, and there pass that cold 

 season in a dormant state, as snakes, lizards, and some other animals do, Mr. C. 

 was the more solicitous to come at the truth. But as these sandy precipices, in 

 which these martins build, are mostly inaccessible, some years passed before he 

 could find a situation where the experiment could be fairly made, without diffi- 

 culty or danger. Such a sand-hill he found in the parish of Byfleet in Surry. 

 The clergyman being his friend, and well qualified to make the experiment, at 

 his request, was so obliging to undertake it. He gives his letter in his own 

 words. 



* Byfleet, October 22, 1757. 

 * Dear Sir, ' 



' I took a square of about 12 feet, over that part of the clifF where the holes 

 were thickest, which in going down from the surface, I judged would take in 

 about 40 holes. I set to work, and came to the holes; but found no martins, 

 nothing but old nests in the farthest end of the holes, which were from a foot 

 and half to two feet and half deep from the entrance. We carefully searched 40 

 holes, but found no birds ; but at least 30 of them had nests. The passage to 

 them was very near in a straight horizontal line; the nest was sunk about an 

 inch and half below the level of tlie passage; the materials next the bottom were 

 straws, then coarse and fine grasses ; the whole structure of no great elegance. 

 The few eggs that were left behind were of a clear unspotted white, the size of a 

 robin-red-breast's.' 



This fair trial, being made by a gentleman of veracity and ability, is very con- 

 clusive; for it certainly proves that the sand martins do not take up their winter 

 abode in their summer dwellings. Therefore there is sufficient reason to believe 

 from the before-recited observations on the common swallows, and this so re- 

 cently made on the sand martins, that they are all birds of passage. 



Additional Remark. — There are 4 distinct species of birds that go under the 

 general name swallow; viz. the swift or black martin; 2, the swallow, that builds 

 in chimneys; 3, the martin that builds against houses ; 4, the sand martin, that 

 builds in sand-banks. Mr. C. thinks he has clearly proved that some of these 

 species are birds of passage. But some of his friends assert that they pass the 

 winter in cliffs or caverns of the earth, in banks or precipices. What is much to 

 be regretted is, that the gentlemen were not curious enough to distinguish the 

 particular species which they found in a torpid state. Mr. Adanson, in his ac 

 count of Senegal, has omitted this. So that nothing certain can yet be pro- 

 nounced, which species stays, or which goes. 



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