OF SELBORNE. 199 



the bank, and was of a different colour 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 never 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 for- 

 wardness for next spring, is allowing perhaps too much fore- 

 sight and rerum prudentia to a simple bird. May not the 

 cause of these latebrce being left unfinished arise from their 



SAND MARTIN S NEST. 



meeting in those places with strata too harsh, hard, and 

 solid, for their purpose, which they relinquish, and go to a 

 fresh spot that works more freely? Or may they not in 

 other places fall in with a soil as much too loose and mould- 

 ering, liable to founder, and threatening to overwhelm them 

 and their labours ? 



One thing is remarkable that, after some years, the old 

 holes are forsaken and new ones bored ; perhaps because 

 the old habitations grow foul and fetid from long use, or 

 because they may so abound with fleas as to become unten- 

 antable. This species of swallow moreover is strangely 

 annoyed with fleas : and we have seen fleas, bed fleas (Pulex 



