SAND-MARTIN. 341 



sion, and keep it too, against all tlie efforts of the poor 

 ill-treated martins and their friends, to expel the 

 intruders. In chalk and gravel-pits, however, they are 

 subject to many dangers from the fall of the soil, 

 whether slipped by accident or intentionally broken 

 down ; and although the upper margin of the pit from 

 its softer material is usually most densely popiilated, 

 yet many pairs, in seeking for similar facilities, build 

 so low down that the holes are easily accessible to 

 boys, or the pickaxes of the men at work in the 

 cuttings. The noted chalk-pits at Horstead, near 

 Norwich, are the resort of immense numbers of these 

 birds, and it is extremely interesting to observe how 

 instinctively they avoid the harder and more stony 

 layers, whilst the smallest portions of the softer strata 

 are selected wherever they may chance to crop out. 

 The nest holes are by no means of the same size or 

 shape, but vary according to the difficulties met with 

 in excavating, and many may be seen left unfinished 

 where a large stone, or other substance too hard for 

 their bills, has obliged them to desist. The depth to 

 which many of these little burrows extend is very 

 remarkable, as I have frequently been unable to reach 

 the nest even at arm's length, whilst others extend from 

 two to three feet into the soil and are by no means 

 always in a straight line, but curved so as to avoid any 

 obstruction in the passage. They have generally two 

 broods in the year, the first flying in June, and the 

 second towards the end of July, as I have found the 

 young still in the down by the second week in July, and 

 eggs hard set upon at the same time. The nests are 

 formed of short bits of straw and grass loosely put 

 together, and lined with feathers — white ones, whether 

 by choice or accident, always largely predominating. 

 In autumn both old and young congregate toge- 

 ther in their pleasure-flights, skimming over the rivers 



