
744 STRATIGRAPHICAL GEOLOGY. [Book VI. — 
the deposition of the overlying Permian rocks. So great indeed was 
the erosion that the Permian sandstones are sometimes found resting 
even on the Carboniferous Limestone. In North Staffordshire the © 
depth of Coal-measures is about 5000 feet, which in South Lancashire ~ 
increases to 8000. These great masses of strata diminish as we trace 
them eastwards and northwards. In Derbyshire.they are about 2500 
feet thick, in Northumberland and Durham about 2000 feet, and about 
the same thickness on the west side of the island in the Whitehaven 
coal-field. In Scotland they attain a maximum of over 2000 feet. 
The Coal-measures are susceptible of local subdivisions indicative of 
different and variable conditions of deposit. The following tables show 
the more important of these : 
SoutH LANCASHIRE. 
GLAMORGANSHIRE. CENTRAL SCOTLAND. 
Feet. Feet. Feet. 
Upper series: sand- Upper series: shales, Upper red Sand- 
stones, shales, &c., red sandstones, stones and clays, 
with 26 coal-seams, Spirorbis lime- with Spirorbis lime- 
more than . 3400 
Pennant Grit: hard, 
thick-bedded sand- 
stones, and 15 coal- 
seams 
Lowerseries: shales, 
3246 
stone, ironstone, 
and thin coal 
seams 1600 to 2000 
Middle series: sand- 
stones, shales, clays, 
and thick coal- 
stone, upwards of . 150 
True coal measures: 
sandstones, shales, 
fire - clays, with 
bands of  black- 
band, ironstone, 

ironstones, and 34 seams. The chief and numerous 
coal-seams . 450 to 850 | repository of coal seams of coal. 
— 3000 to 4000 | Thickness in Lan- 
Millstone Grit. Lower or Gannister arkshire upwards 
series: flagstones, of...) Lea ae 
shales, and thin 
coals. . 1400 to 2000 | Moor Rock, or Millstone 

Grit. 
Millstone Grit. 
The numerous beds of compressed vegetation form the most remark- 
able feature of the Coal-measures. As already stated each coal seam is 
usually underlaid by a seam of fire-clay (mur of the Belgian coal-fields), 
which, traversed in all directions by rootlets, and free or nearly free of 
alkalies and iron, is the soil on which the plants that formed the coal 
grew. <A coal-seam accordingly marks a former surface of terrestrial 
vegetation, and the fissile micaceous sandstones that overlie it show the 
nature of the sediment under which it was eventually buried. 
The Coal-measures of Britain have not yet been very precisely 
subdivided into paleontological zones. ‘The lower portions or Gan- 
nister beds of Lancashire contain at least 70 species of undoubtedly 
marine fossils (Goniatites Listeri, six species of Nautilus, Aviculopecten 
papyraceus, Lingula squamiformis, &c.), together with such shells as Anthra- 
cosia, probably indicating brackish water. The middle and upper 
divisions are characterized by the prevalence of species of Anthracosia, 
Anthracoptera, and Anthracomya. Some of the more characteristic fishes 
are Strepsodus sauroides (Vig. 353), Rhizodopsis sauroides, Megalichthys 
Hibberti, Cheirodus granulosus (Fig. 353), Janassa linguiformis, Ctenacanthus 
hybodoides (Fig. 342), Pleuracanthus leevissimus, Otenoptychius apicalis, Some 
species range from bottom to top of the Coal-measures—e.g. Ctenoptychius 
pectinatus and Gyracanthus tuberculatus.} 
On the Continent of Europe the Carboniferous system occupies 
1 My friend Dr. Traquair has been kind enough to furnish me with information on 
this subject which he has so carefully studied. 
