CARBONIFEROUS. 



147 



Evidences of volcanic activity have been met with in the 

 Lower Carboniferous rocks, but no contemporaneous eruptive 

 rocks are known in this country, higher up in the series. 



The following Table exhibits the chief divisions of the Car- 

 boniferous System in this country : — 



Q^ 



Devonshire. 



Culm- 

 measures. 



Pilton, 



Baggy, and - 



Marwood 



Beds. 



Pickwell 

 Down 



Sandstones, 

 etc. 



South Wales and 

 Somersetshire. 



Derbyshire and 



Yorkshire. 



N. IV. Cumberland 



and 

 Noi-thumberland. 



Coal-measures. 

 Millstone Grit. 

 Upper Limestone Shales. Yoredale Rocks. ^ Bernician and ^ 



Calciferous 

 Carboniferous Limestone, 



Lower Limestone Shales, 



Sandstone 



Series 



(Tuedian 



Beds). 



Upper Old Red Sandstone and Conglomerate. 



O 



Although connected with the Upper Old Red Sandstone 

 by gradations that forbid any sharp line of demarcation being 

 drawn, yet the organic remains of the succeeding Carboni- 

 ferous rocks are distinct from those of the Old Red Sand- 

 stone, and the beds were evidently deposited under different 

 physical conditions. The area in which they were accumu- 

 lated was, on the whole, a subsiding one, during a long 

 period of time. Thus in South Wales, in proceeding westwards 

 from Llandeilo, it has been pointed out by De la Beche, that 

 the (Upper) Old Red Sandstone begins to overlap the Silurian 

 rocks, and to rest directly upon older strata. Still further 

 west the Old Red Sandstone is overlapped by the Carboniferous 

 Limestone, which again near Haverfordwest is overlapped by 

 the Coal-measures, the latter thus resting in that neighbour- 

 hood on the Cambrian rocks.^ 



The arenaceous deposits of the Upper Old Red Sandstone 

 were perhaps laid down in large lakes or inland seas. Deeper 

 and more open sea conditions attended the deposition of the 

 muddy sediments that now form the Lower Limestone Shales 

 of the West of England ; while still deeper and clearer marine 

 conditions prevailed locally during the accumulation of the 

 Carboniferous Limestone, with its rich beds of Crinoids and 

 Corals and Brachiopods. The Corals formed part of old 



Mem. Geol. Survey, i. 24. 



