16 A NEW FLORA OF 



Burn ; other good coals, such as the Bensham, Beaumont, and 

 Brockley, are worked in collieries west of Newcastle. Several 

 seams are now worked in the neighbourhood of Sunderland, where 

 the overlying Magnesian Limestone has been pierced to reach 

 the Carboniferous beds : one pit there is 1800 feet deep. 



Though some of the posts or sandstones are thick, one being 

 84 feet, yet the proportion of shales is greater in the Coal Mea- 

 sures than in the Mountain Limestone. Assuming the total 

 thickness of these measures to be 2000 feet, then we have 80 

 feet of coal, 960 feet of sandstone, and 960 feet of shale ; and 

 from this large amount of argillaceous matter, the soil of the 

 Coal Measures is more moist and clayey than that over either 

 the Millstone Grit or the Mountain Limestone, and the scenery, 

 too, is of a tamer character, with fewer bold cliffs and high hills. 

 The low portions of the undulating ground are mostly valleys of 

 denudation ; for where the thick argillaceous strata have cropped 

 out the soft material has been swept away, and the surface hol- 

 lowed by denuding agencies, leaving the harder sandstones as 

 low rounded hills. 



1^0 undoubted marine organisms appear in these Coal Measures, 

 excepting one Brachiopod {Lingvla mytiloides), which was found 

 by Mr. Kirkby in a bed of shale, at By hope colliery, 680 feet be- 

 low the Magnesian Limestone ; but this genus seems to have 

 had the capacity of living in brackish water, probably in an es- 

 tuary, for we find it also in the Mountain Limestone associated 

 with coal seams, along with Anthrocosia and fish remains. Of 

 fishes several species have been found in different zones, such as 

 Gyracantlius formosus and tuhereulatus, 3IegalicMhyH HiMerti, 

 Diplodus gihhosus, CtenoptycJiius pectinatus and dmticulatus, and 

 species of Paleeoniscus, Platysonius, Rhizodus, Aniblypterus, Or- 

 thacanthus, Leptacanthus, &c. The successful researches of Mr. 

 Kirkby and of Mr. Atthey have extended our knowledge of the 

 Ichthyology of the Coal Measures. From sections of jaws and 

 teeth, prepared by Mr. Craggs, and found in the shales and coal 

 of the Low Main Seam, Professor Owen has recently described 

 eleven new genera of fishes about the size of the minnow, 

 one of which is of the Sauroid type ; and associated with them 



