below the Bottom coal of 37 feet (excluding trap) there is "Singing coal 4 feet." If from this we take off a portion to include the Gubbin and Balls, &c., the remaining thickness will be very nearly equal to what these beds have near Wolverhampton.
In some parts between Wolverhampton and Bilston I believe the Singing or Mealy-greys coal is now "gotten" (1852), and is looked on by the iron-masters as a valuable help to their resources.
The materials composing the beds just described are generally an alternation of fire-clay, clunch, or binds, with rock or rock binds, sometimes the argillaceous, sometimes the arenaceous character predominating. In the neighbourhood of Bentley one or two little coals a few inches thick likewise show themselves.
37. Measures between the Mealy-grey coal and the Blue-flats ironstone.—Below the Singing or Mealy-grey coal we get a mass of beds consisting sometimes entirely of fire-clay, more frequently of alternations of fire-clay and rock, varying in thickness from 16 feet to 50 feet, before we reach the Blue-flats ironstone. As in the case of the beds above described, these measures are also thickest in the Bentley district, where they contain also one or two little beds of coal, and in their lowest portion some ironstone balls. The alteration in thickness in these beds is sometimes rapid, as in a colliery at Portobello near Wolverhampton, in two pits within 150 yards of each other, the beds consisting in both of fire-clay and rock, varied from 16 feet to 29 feet in thickness. Elsewhere about Wolverhampton they have a pretty constant thickness between 20 and 25 feet.
The two groups of beds, namely, those above and those below the Singing or Mealy-grey coal, while they each vary in thickness in different places, usually vary in such a way as to balance each other and maintain a certain mean aggregate thickness.
The aggregate thickness of the whole beds between the Gubbin and Balls, and the Blue-flats ironstones is, near Wolverhampton, never more than 53 feet nor less than 40 feet (exclusive of trap); but north and east of Willenhall, around Bentley, and up to Bloxwich, it is never less than 70 feet, and sometimes reaches 85.[1]
It will be important to bear these facts in mind when we come to describe the trap rocks which have been intruded into these beds.
38. to 42. (I. 14, 15, 16.) The Blue-flats ironstone, together with the Diamonds and Silver threads ironstones.—We have now to describe the lowest recognizable measures in the whole of the South Staffordshire coal-field, those beneath which neither coal nor ironstone have ever been found that were of the least value.
The Blue-flats ironstone is confined absolutely as a workable measure to the district between Wolverhampton and Walsall, scarcely going south of Bilston, nor so far north as Bloxwich. It is an easily recognizable ironstone, as it occurs usually in regular bands a few inches thick, which are smoothly jointed, and are but slightly concretionary in structure. When brought to the pit bank the lumps of ironstone look like large rather irregular bricks; they are pale brown at first, but from
- ↑ In Samuel Arblaster's pit near the Brown Hills before mentioned, they got some ironstone somewhat resembling the Blue flats at a depth of only 12 feet (white tender rock) below the supposed Gubbin and balls. The identification of the measures, however, is too doubtful for us to found any argument on.
