The Wall-swallow, who is much less common than the other, never chooses a site within our houses for his structure. It must be outside for him and it must stand high, far removed from inquisitive eyes; but at the same time a shelter against the rain is indispensable, for the damp is almost as dangerous for his mud nest as for that of the Pelopæus. He therefore settles by choice under the eaves and cornices of buildings. He visits me every spring. My house pleases him. Just below the roof is a cornice made up of a few courses of ordinary “half-round” coping-tiles, corbelled out from the face of the wall in such a way as to give a long line of round-headed niches which are sheltered from the rain and enjoy plenty of sunshine on the south front. Among all these nooks, so healthy, so well-protected and moreover so excellently adapted to the shape of the nest, the bird has only to choose. There is room for all, however numerous the colony may become one day. Apart from sites of this kind, I see none approved by the Swallow in the village, except the under part of a few cornices of the church, which is the only edifice of a monumental character. In short, the support of a wall, in the open air, with some shelter against the rain, is all that the Swallow asks of our buildings. But the natural wall is a perpendicular rock. If the bird here finds overhanging projections, forming a penthouse, it must adopt them as the equivalent of the ledge of our roofs. Ornithologists know, in fact, that in mountainous districts, far removed from human dwellings, the Wall-swallow builds against the vertical sides of the rocks, so long as his ball of clay is under cover of some kind. Near where I live are the Gigondas Mountains, the most curious geological structure that I have ever seen. Their long chain displays so steep a slope that it is almost impossible to stand upright near the summit; and the ascent of the accessible part has to be made on all-fours. You then find yourself at the foot of a perpendicular cliff, an enormous slab of sheer rock which, like some Titanic rampart, tops the precipitous ridge with a jagged crest. The people of the country call this Cyclopean wall les Dentelles. I was one day botanizing at its base, when my eyes were attracted by the evolutions of a flock of birds in front of the rugged face of the rock. I easily recognized the Wall-swallow: his silent flight, his white belly and his ball-shaped nest fastened to the cliff told me all about him. I in my turn now learnt, apart from the books, that this species fixes its nests to perpendicular rocks when the cornices of our buildings and the ledges of our roofs are missing. Even so must it have nested in the ages that preceded our stone structures.