Geology of the South-east of Devonshire. 



473 



tain manganese, and it is found in them from whatever part of the world they are brought. This cir- 

 cumstance would seem to indicate that the manganese has been given off by the trap ; but the quantity 

 of that earth contained in trap rocks has never been ascertained to exceed 0*25, whilst we constantly find 

 bunches of metal of great extent and richness associated with dykes of inconsiderable bulk. 



Fig. 14, which was taken from a road-section near Pulser, represents a mode of 

 occurrence distinct from the cases already described ; the mass of trap (a) is evi- 

 dently intrusive, on account of the broken edges of the slate surrounding it, but 

 it was, previously to its protrusion, compact and jointed. There is much trap in 



Fig. 14. 



b Slate. 



Trap a. 

 Section near Pulser, junction of trap and slate. 



the higher parts of the same ridge, which was evidently in a fluid state when it 

 reached the surface. All masses in that condition at great depths, may have por- 

 tions nearest to the solid crust in various stages of temperature, and some suf- 

 ficiently cooled to be soUd rock ; so that whenever any disturbance should force 

 the liquid mass amidst sedimentary deposits at the surface, portions of the mass 

 which, had already become solidified below, might also be brought up along with, 

 or forced laterally among, such deposits. In this case, a greater amount of dis- 

 turbance might be expected than when the entire body of trap was fluid ; but at 

 Petit Tor is an analogous case, where large angular blocks of limestone have been 

 forced laterally into the slate, and have merely crushed the edges of the beds im- 

 mediately about them. 



Carbonaceous Epoch. 



§ 1 . Interstratified. — Volcanic products are interstratified with the beds of this 

 series, in the same manner as in the older slates, presenting analogous minera- 

 logical characters and modes of association. The phsenomena indeed are identical, 

 and prove, that in some quarters, volcanic agents continued in operation after that 

 change (whatever it was), of which the character of the organic contents of the 

 two deposits is the permanent evidence ; being purely marine in the one, and 

 partly terrestrial in the other. The broad and frequent bands which are associated 

 with the lowest carbonaceous beds along their southern boundary, and which are 

 more considerable than any trappean masses interstratified with the older slate 

 rocks, seem to indicate that the change was accompanied by even increased vol- 



