l8o CARBONIFEROUS. 



Coleoptera {Curculioides) and PalcEodidyopfera {Brodia, ArchcEoptilus, 

 and Etoblattina, a kind of Cockroach) ;^ IMyriapods such as Xylobuis, 

 and Arachnida, Eoscorpius (Scorpion), Eophiynus; Fishes, Mcga- 

 Uchthys, Ctenodiis, AcantJiodes, Plcuracaiithus, Lepracanthiis (Ichthyo- 

 dorulites), Rhizodus (i6 to i8 feet in length) and Ccelacanthus; and 

 upwards of 30 Labyrinthodont Amphibia, including Pholiderpeton, 

 Archegosaurus, Parabatrachus, Anthmkerpefoii, etc. ]\Ir. R. Etheridge, 

 jun., has pointed out that the Tubicolar Annelide Spirorbis pusilliis 

 was not necessarily marine ; but may have been able to live in 

 freshwater.'^ The undoubtedly marine fossils found in the Coal- 

 measures are limited to a few horizons, and these, as before 

 mentioned, belong chiefly to the Lower division.^ 



The Coal-measures are frequently divided (as are most other 

 formations) into the Upper, INIiddle, and Lower Series ; the Upper 

 and Middle divisions being regarded as essentially freshwater 

 (lacustrine) and estuarine. These divisions, while noted in 

 different Coal-fields, cannot be regarded as corresponding with any 

 minute accuracy in different areas. 



The term Coal-field is applied to the several geographical tracts 

 over which the Coal-measures are exposed, including the area they 

 occupy beneath newer strata, where they are so connected as to 

 form one field ; but many of the different coal-fields may be 

 connected at great depths beneath newer strata. The total area of 

 the coal-fields in England and Wales is estimated at about 3000 

 square miles. 



I. NORTHUMBERLAND AND DURHAM COAL-FIELD. 



This coal-field extends from the River Coquet, near Warkworth, 

 to Morpeth,^ Newbiggin, Newcastle, North and South Shields, 

 Jarrow, and Durham, across the valleys of the Tyne, Wear, and 

 Tees, to Bishop Auckland. The strata are thus divided : — 



Upper Series, with thin coals and a band of ironstone, 900 feet. 



Middle Series, with thick coals, from the High Main Coal to the Brockwell 



Coal, 2000 feet. 

 Lower Series, with two beds of coal, between 2 and 3 feet thick, 150 feet. 



The High Main and Low Main are the most important coal- 

 seams : they are from 3 to 6 feet in thickness. The Hutton seam, 

 from 2 to 4 feet 6 inches in thickness, is noteworthy as yielding 

 good household, gas, and steam coal. 



1 S. H. Scudder, Geol. Mag. 18S1, p. 293 ; and 1885, p. 265. 



2 G. Mag. 1S80, pp. 113, 219. 



3 E. Hull, Q.J.G.S. xxxiii. 615. 



* One of the earliest descriptions of this district was by N. J. Winch, T.G.S. 

 iv. i. The Coal-field has also been illustrated by John Buddie, Nicholas Wood, 

 Westgarth Forster (1821), and others. See G. A. Lebour, Geology of Nor- 

 thumberland ; J. B. Simpson, Sections of the Northumberland and Durham 

 Coal-field, 1S77 ; J. W. Kirkby and J. Duff, Nat. Hist. Trans. Northumberland, 

 etc. iv. 150. 



