GEOLOGY. 87 



Coal Strata, locally ascertained. 



T . ("Clavs and Sandstone, 



Maarnesian Limestone, or \ A -. 



< Gvpseous Marl, and 



Zecbstem i % i ci * 



( Marl Slate. 



New Red Sandstone, or ( Variegated Clays and Sand- 



Poikilitic group \ stones. 



Lias Shale and Lias Limestone. 



( Portland Oolite, Kimme- 

 3 rid S e Cla ^ Coralline 



^ f~ 1 .. /-i l /-i * A 



J Oolite, Calcareous Grit, 

 (. Sand, and Oxford Clay. 



Weald f Weald Clay, Hastings 



\ Sands, & Purbeck Beds. 



Green Sand Green Sand and Gault. 



r , ,, ( Upper and Lower Chalk, 



" I Chalk Marl. 



THE OLD RED SANDSTONE is the lowermost of the 

 secondary series, which, although it principally consists 

 of sandstone, yet it comprises in various localities marls 

 and limestones. Conglomerates, or pudding stones, belong 

 to this stratum : they consist of pebbles conglutinated 

 together with some mineral substance. The red colour 

 is given to this sandstone by the oxide of iron which it 

 contains. The Old Red Sandstone is occasionally seen 

 from Wales to the North of Scotland ; in Herefordshire, 

 Worcestershire, and neighbourhood ; and it is of im- 

 mense thickness, being sometimes not less than 10,OOO 

 feet. There are very few fossils in marls and sand- 

 stones, where the oxide of iron prevails. 



MOUNTAIN LIMESTONE is of a grey crystalline cha- 

 racter, and contains marine shells and corals. This 

 stratum is in some places nearly 3,000 feet thick. Moun- 

 tain limestone forms common lime, perfectly white ; 

 the animal and vegetable matter which rendered it dark 



O 



being destroyed by the process of burning. 



COAL. The coal measures are the most useful pro- 

 ductions of the globe, and abound in the northern and 

 western parts of England. The depth of the strata is 

 said to be, in some instances, from 4,000 to 5,OOO feet, 

 containing numerous beds or seams of coal from half an 



