THE CARBONIFEROUS SYSTKM L"Jf> 



The Millstone Grit consists of several sets of grits and flag- 

 stones separated by shales of varying thickness. Its thickness 

 increases to the northward, and finds its maximum in East 

 Lancashire and the adjacent part of Yorkshire, where it is said to 

 be over 3500 feet thick. Throughout the northern part of the 

 area the following subdivisions can be traced, though the thickness 

 of each varies greatly : 



First grit or rough rock. 



Shales. 



Second grit. 



Shales. 



Third or Chatsworth grit. 



Shales. 



Kinderscout grit, or fourth grit. 



The lowest grit takes its name from the high tableland of 

 Kinderscout in the Peak country, which consists of this rock and 

 rises to a height of 2000 feet above the sea. The third grit forms 

 long conspicuous escarpments on both sides of the central area. 

 The second grit is less persistent than the others, or rather the 

 shales above thin out so that it coalesces with the first grit The 

 Rough Rock is a very coarse grit, sometimes passing into a con- 

 glomerate of small quartz pebbles. In Lancashire it contains a 

 workable coal-seam called the " Feather-edge coal" The shales 

 below also include thin seams of coal. To the south-west in 

 Staffordshire the middle grits thin out, but the fourth grit appears 

 to be represented on Congleton Edge by a set of grits and shales 

 about 500 feet below the third grit, so that the group here is not 

 less than 1000 feet thick, and has the Pendleside shales below it. 



Still farther south the grits thin out entirely, and they do not 

 appear in the South Staffordshire or Warwickshire coalfields. In 

 Nottingham also they thin southward and have nearly disappeared 

 at Ashby de la Zouch, in Leicestershire, where only 50 feet of such 

 grit is left at the base of the series. A similar small tongue of grit 

 reaches to the Wellington district of Shropshire and then thins 

 out. 



Lower Coal-Measures. These are sometimes called the 

 Gannister measures, gannister being the miners' name for a peculiar 

 hard and compact siliceous underclay (or fireclay) which often forms 

 the floors of the coal-seams. Hard grey flagstones are the pre- 

 dominating beds in this division, with subordinate bands of shale. 

 The coals are generally thin, but two or three from 3 to 4 

 feet thick are often worked. In the vicinity of the coal-seams 

 plant remains are abundant, but the fossils in the other beds are 

 generally marine forms (see p. 293). 



