FT. | FT. | ||||||||||||
19. | (I. 6.) | Intermediate measures containing, at Bentley, the ironstones known as the Lambstone and Brownstone | from | 10 | to | 33 | |||||||
20. | (I. 7.) | New Mine or White ironstone | from„ | 2 | to | 10 | |||||||
21. | (I. 8.) | Measures containing the Penny-stone ironstone called also Bluestone or Cakes | from„ | 10 | to | 25 | |||||||
22. | (XIX.) | Sulphur coal | from„ | 2 | to | 9 | |||||||
23. | Intermediate measures | from„ | 3 | to | 99 | ||||||||
24. | (XX.) | New Mine coal[1] | from„ | 2 | to | 11 | |||||||
25. | (I. 9.) | Measures containing the Fireclay Balls ironstone occasionally | from„ | 2 | to | 40 | |||||||
26. | (XXI.) | Fireclay coal (and partings) | from„ | 1 | to | 14 | |||||||
27. | Intermediate measures | from„ | 2 | to | 10 | ||||||||
28. | (I. 10.) | Getting Rock ironstone (occasional) | from„ | 4 | to | 5 | |||||||
29. | (I. 11.) | Poor Robin ironstone measures | from„ | 3 | to | 5 | |||||||
30. | Intermediate measures, sometimes wanting | from„ | 0 | to | 9 | ||||||||
31. | (I. 12.) | Rough hills White ironstone (occasionally) | from„ | 2 | to | 19 | |||||||
32. | (XXII.) | Bottom coal | from„ | 3 | to | 12 | |||||||
33. | Intermediate measures | from„ | 5 | to | 30 | ||||||||
34. | (I. 13.) | Gubbin and Balls ironstone, sometimes called the Great or Bottom Gubbin | from„ | 3 | to | 10 | |||||||
35. | Intermediate measures | from„ | 18 | to | 50 | ||||||||
36. | (XXIII.) | Singing or Mealy Grey coal (occasional) | from„ | 2 | to | 4 | |||||||
37. | Intermediate measures | from„ | 16 | to | 50 | ||||||||
38. | (I. 14.) | Blue Flats ironstone | from„ | 2 | to | 9 | |||||||
39. | Intermediate measures | from„ | 10 | to | 14 | ||||||||
40. | (I. 15.) | Silver Threads ironstone | from„ | 4 | to | 7 | |||||||
41 | Intermediate measures | from„ | 6 | to | 15 | ||||||||
42. | (I. l6.) | Diamonds ironstone | from„ | 2 | to | 3 | |||||||
43. | Lowest measures, maximum thickness known below the Diamonds ironstone | about | 50 |
The variations in thickness, noted in the preceding general section do not take place indiscriminately, but chiefly according to a general rule, the least thickness being almost invariably found to the south, while the greater thicknesses come in regularly as we proceed northwards. There are, however, local exceptions to this statement, in the fact of a sudden thickening or thinning of any particular group of beds in a partial manner, and over a small area, with an immediate return to the normal thickness of the neighbourhood. The group of sandstones known as the Thick-coal rock, and some other sandstones, have these partial thickenings, while the shales between the New Mine and Fire-clay coals, sometimes, as in the Stowheath field, diminish quite unexpectedly to two feet, and then suddenly regain their usual dimensions of 30 or 40 feet. Sometimes, indeed, these two coals are so split up by partings, that when the thickness between
- ↑ The New Mine coal is completely separated into two coals at Bentley, there called the Three-foot and the Five-foot, with 33 feet of shale and sandstone, containing ironstone between them.