Geology of the South-east of Devonshire, 



455 



manganese, but the latter only in a small proportion ; and it may be some help 

 towards the solution of this point to mention, that wherever limestone blocks and 

 pebbles occur (as about Teignmouth), the materials which surround them are not 

 coloured. Now either the whole mass was red throughout, and the colour of the 

 portions in contact with the limestone subsequently discharged, or the colour must 

 have been at some time subsequent to the accumulation of the deposit imparted to 

 all the mass, except to such portions as happened to be in contact with fragments of 

 limestone ; the latter supposition seems most reasonable. If we examine the coloured 

 portions, we observe that each particle is coated with a thin pellicle of peroxide of 

 iron : now as this could not have been held in solution by the water which collected 

 the materials, we must suppose that the conditions under which they were sub- 

 sequently placed, favoured the conversion of the iron contained in the abraded 

 porphyritic rocks, and at first only mechanically disseminated throughout the mass, 

 into colouring matter for the whole of it, with the exception already noticed. 



A jointed structure, the joints having a constant direction, is not distinctly marked throughout all 

 portions of this formation, and the nature of the deposit does not admit of its being observed as easily 

 as in some other rocks ; yet lines belonging to a system of joints may occasionally be traced even among 

 the conglomerates, as beneath the Ness at Teignmouth. 



Near Sidmouth these divisional lines are particularly well marked, and may serve as a general 

 illustration. 



Fig. 7. 



21 feet. 



12* feet. 23 feet. U ft. 24 feet. 



Joiuted and Cleavage Structure, New Red Sandstone near Sidmouth. 



The above diagram represents a ground-plan of rocks of fine-grained fissile sandstone, exposed at low 

 water, and exhibits six lines of joints (a to /), ranging 1° 30' west of true north, at intervals of 

 21 ft., 12 ft. 6 in., 23 ft., 1 ft. 6 in., and 24 ft. The strike of the beds is marked by a seam of sulphate 

 of lime X, running N.W. and S.E., and the other lines parallel to this are those of the partings of the 

 laminae. 



3 N 2 



