Summer Birds of Passage. 461 
which is a precarious and treacherous cause. 
For the sense of want would not fail in many 
instances to invite these animals to certain 
death in the midst of frost and snow, at an 
earlier season than the commencement of 
spring, If we suppose our known sleepers, 
or any other animals suspected of torpid 
habits, to retire to a depth less than 80 feet, 
but to a distance from the surface which is 
sufficient to conceal them, in damp and dreary 
grottos, from human observation; the suppo- 
sition will not remove the difficulty. For the 
time when our periodical quadrupeds, birds, 
and reptiles disappear, coincides with the 
maximum of temperature in such places, and 
they are seen abroad again when the same 
temperature is at the lowest. 
Very few arguments will be now required 
to demonstrate the impessibility of the ana- 
logy which is supposed to connect the pe- 
riodical birds of summer, and the sleeping 
animals of winter. It is sufficient barely to 
iémark; that the former are’ never found 
slumbering with the latter, near the sur- 
face of the earth; and deep caverns are 
proved to be unfit for the reception of 
any creature in the torpid season.  Con- 
sequently the birds in question, desert the 
