Page:The South Staffordshire Coalfield - Joseph Beete Jukes - 1859.djvu/96

78 exposure to the air assume a dull blue or purplish look. This colour, joined to the flat pavement-like form in which they are found below, gives them their name.

The ironstone usually occurs near Wolverhampton in two, three, or four regular bands, interstratified with clunch or clod, as in the following sections:—

The Blue flats are mentioned with a thickness of about 3 feet a Deepfields and Bradley, and as 5 feet thick at Darlaston; but what proportion of ironstone they contain there I do not know.

In some places near Wolverhampton mention is made of the "Bristol diamonds ironstone" just below the Blue flats. It seems there to be very poor and trifling; but ns we proceed to the north-east we find around Bentley and Walsall the Diamonds ironstone as rich and important ns the Blue flats, and, moreover, the "Silver threads" coming in between them, with much ironstone in bands and cakes in the intervening