'PROCREANT CRADLES' 115 



ciple of the arch, each part of the curve supporting the rest, 

 and all propped on the rock. But when the growing nest 

 consists of a mere ring on the upright and almost smooth 

 rock, it is impossible to get much support from the thrust of 

 any part of it on the rocky surface, and all depends on the 

 skill with which the dipper packs the wet moss firmly into 

 place. The growth of a dipper's nest in such a place is a 

 remarkable sight. Wrens, which build a globed nest much 

 like the dipper's, also have great skill in hanging it to a 

 slight foundation. They can twine the foundation to a 

 support not very much less smooth and forbidding than the 

 dipper's rock, such as a shallow hollow in the trunk of an 

 oak-tree, or the side of an earthy bank. Even the blackbird 

 sometimes displays a successful persistence in lodging a nest 

 on a sloping surface where the force of gravity is very 

 unfriendly to the enterprise. Such a position is provided by 

 a horizontal rafter with a surface sloping outward at just 

 such an angle that a few straws will rest upon it, but a mass 

 of them fall off by their own weight. When this happens, 

 the blackbird tries again ; and with a glimmer of mistaken 

 intelligence, it usually tries not in the same position — ' That 

 was a bad place ' it seems to say — but a foot or two further 

 along. Sometimes there are half a dozen half-built nests 

 collapsed in a row before the blackbird succeeds in getting 

 one to stick — not as it fondly seems to imagine, by the 

 superior retentiveness of the site, but because chance or 

 skill led it to bring more suitable materials or place them 

 more wisely. If the blackbird used mud for the foundations 

 of its nest, instead of for its central stiffening, the task of 

 fixing it to a beam might be as simple at the beginning as 

 the swallow's. But blackbirds and thrushes lay the founda- 

 tions with twigs, bents, and locks of wool or moss, adding 



