Physical Structure and older stratified Deposits of Devonshire. 661 



the continual clianges of mineral structure, no two distant sections can agree in their more minute 

 details. The further range of the arenaceous series westward seems to be marked by the hard, 

 irregularly bedded, gray quartzose rocks of Morleigh Down and Black Down, first noticed by 

 Mr. De la Beche*. 



2. Over the preceding group, and not separated from it by any well-defined limit, is expanded 

 a slate formation of vast thickness. Soft glossy chloritic slates prevail, and alternate with arena- 

 ceous bands, and near Rediop Cove with a remarkable ferruginous whet-slate. Near Stoke there 

 are some beds of flaky or semiconcretionary structure, like many beds associated with contempo- 

 raneous porphyries in Wales and Cumberland. Here, however, we saw no traces of trappean 

 rocks. A little south of Stoke are some very fine beds of chloritic slate, exhibiting those wavy lines 

 among the laminae, which produce what we have called a false stripe ; but there were no examples 

 of an oblique slaty cleavage. For a considerable way north of Street the dip is reversed to N.N. W., 

 but soon after recovers, and dips about magnetic south at a great angle. No calcareous beds fit 

 for use are found in this series ; but near Slapton it is overlaid by horizontal masses of new red 

 conglomerate, which has been burnt for lime. 



Near Torcross the dip is reversed to the north ; and in a cliff to the south of it is a gray, 

 greenish gray, and blue slate, with many quartz veins, generally parallel to the beds, but continually 

 thinning out and running into filamentous veins. With these beds we found some long, flat, cal- 

 careous concretions : but we did not observe any organic remains, in this or any other part of the 

 group. On the whole, the mineral phenomena, on this part of the coast, though differing in a 

 thousand accidents, agree in all their essential circumstances with those exhibited by the corre- 

 sponding group in Bigbury Bay. 



3. For some way beyond the beds last described, the dip is nearly north at a great angle — on 

 the average not less than 60°. A long flat region then conceals the relations of the strata; beyond 

 which the crystalline group, commencing more than a mile south of Tor Cross, occupies the coast 

 io the extremity of Start Point. The highest beds of this group are nearly perpendicular — they 

 are then thrown into cortortions — and then for a considerable way along the southern cliff have a 

 steady dip to the north at an angle of about 50°. Still further south they exhibit the same modi- 

 fications of mineral structure that we remarked in the cliflfs between Bolt Tail and Prawle Point. 



At their northern limit they are certainly less crystalline than at their southern. Some of the 

 beds contain many elongated concretions of quartz, spangled with flakes of mica or coated with 

 chlorite, alternating with laminae of dark chlorite slate; and associated with these are beds of very 

 fine dark clay slate, of a structure intermediate between the slates of the second group and the 

 crystalline slates of Start Point. It is obvious from what is stated, that there is no true passage 

 between this and the preceding group; nor are the phenomena at the junction so instructive as 

 those which occur at Hope Cove, 



Such is the succession of rocks exhibited in transverse sections of South 

 Devon ; the whole ascending series being divided into four groups : 



1. The slate-rocks bordering on Dartmoor^ many parts of which are indu- 

 rated and altered in structure by the action of the granite. 



* In a traverse from Totness to Kingsbridge we crossed a series of red arenaceous slates which 

 seemed to represent, under a different type, the great upper limestone and its associated red grit. 

 Near Kingsbridge the beds are highly inclined and thrown into great undulations, caused per- 

 haps by the same disturbing forces which produced the undulations near Avon mouth. 



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