104 THE STORY OF THE EARTH. 



out of which the millstone grit sandstone was 

 made. 



The thick deposits in the south of England 

 arc near to the areas in which the thick masses 

 of old red sandstone are found. It is possible 

 that such a cause has governed the thickness of 

 the deposit, though in the west of Pembrokeshire 

 the Millstone Grit is only 300 feet thick; and it 

 is difficult to see in areas now exposed any source 

 for the Kinderscout grits, except in such ancient 

 rocks of Shropshire as form the Longmynd, and 

 the Denbighshire grits of North Wales. Denu- 

 dation of the original materials from which such 



ient rocks as those were derived would have 

 made these sandstones. 



The Cod/ Measures. 



The rocks which yield coal are a succession of 

 sandstones, and shale, ironstones, fire clays and 

 coal seams, which are repeated over and over 

 again. They thicken from Northumberland 

 south-west to South Wales; chiefly owing to in- 

 u quantity of the sand. In the north oi 

 gland the thickness is 1500 feet; in the south- 

 west in Wales it is 11,000 feet. 



I ire 1 ays arc old soils of the carboniferous 



d in which the roots of forest trees often stand 



vertical, as they grew; showing that the coal was 



aty gtOH th, like Irish bogS, due 



the fall of fores! tree-, and the accumulation 



Of Vegetable matter where the forest trees had 



>\A ii. Iii SOU! Ii W a >f torcst 



! the kinds named Sigillaria and 



metmies Ik- -ccii < rushed flat like 



moi her in the posi! 



