The deeper tints are, however, peculiar to the nuptial plumage, or are only to be faintly traced at other times, so that in winter the adults - and the young always - have a much plainer appearance, ashy-grey and white being almost the only hues observable.
The colours range from deep black to pure white, passing through chestnut or bay, and many tints of brown or ashy-grey, while often the feathers are more or less closely barred with some darker shade, and the black is very frequently glossed with violet, blue or green - or, in addition, spangled with white grey or gold-colour.
The original material was a fine clay, sometimes with more or less of sand or ashy ingredients, occasionally with some lime; and the bedding may be indicated by alternating bands of different lithological character, crossing the cleavage faces of the slates, and often interrupting the cleavage, or rendering it imperfect.
1 and 2), of an ashy white colour, with a body in the case of the male not 2 in.
3) is hairless, of an ashy grey or cream colour, attains to a length of from 3 to 32 in., and is slender in comparison with many of its allies.