GEOLOGY 



These bands on coalescing strike westward to the coast at Bolt Tail and 

 Outer Hope, where they form a syncline separating the mica quartz 

 schists of the Bolt from a narrower band of the same series on the north. 

 The mica and quartz schists of the Start district in a complex anticline, 

 therefore, separate the green schists of the Prawle from those of the 

 Bickerton valley. These main structures are rendered shallow by an 

 innumerable series of minor folds, accompanied by gnarling and small 

 thrusts, as shown in the Hall Sands cliff. The minor folds are also 

 indicated by joints, or strain planes, breaking the mica-quartz schists 

 into vertical or horizontal masses, so well shown in the rugged outlines 

 of Bolt Head ; or by isolated synclinal masses of the green schists as at 

 ' Spirit of the Ocean ' Cove near Start Point. The green schists, 

 where they occur in mass, are often intersected by even planes which 

 give them an appearance of bedding, frequently seen to be at variance 

 with the contorted foliation of the rock. 



Although the distinction between these rocks and the grey, com- 

 paratively unaltered, Lower Devonian slates which bound them on the 

 north is everywhere strongly marked, it is hardly possible to fix on any 

 definite boundary in the numerous junction sections afforded by the 

 coasts and the intermediate creeks of the Salcombe estuary. This is 

 due to the presence of an intervening series of rusty brown rocks in 

 which hard carbonates are generally present ; these form a zone, of 

 several chains in breadth, with which both the Devonian slates and the 

 altered groups seem to be connected. The green schists are separated 

 from the Devonian by these brown rocks from Malborough eastward, 

 and from Malborough to Hope, where mica schists bound the Devonian 

 slates, to judge from their presence at Hope Headland and Mouthwell ; 

 though not exposed their occurrence may be assumed. 



At Malborough the mica and quartz schists are peroxidated. At 

 Lannacomb Mill, on the Start coast, they exhibit pinkish and grey tints, 

 and quartz-albite (pegmatite) veins are plentiful. These however occur 

 occasionally in the Lower Devonian rocks. The junction brown rocks 

 seem to be a series of partly calcareous and siliceous materials associated 

 with slates and volcanic rocks, but, apart from the hard carbonates in 

 them, they are too rotten for petrographical investigation. Faults and 

 thrusts occur in these junction rocks, but no evidence of a great thrust 

 plane, or fault, separating the altered and unaltered rocks from east to 

 west has been obtained. 



The altered rocks conform in strike to the Devonian on the north, 

 and there seems to be no proof of their having experienced a prior 

 movement to that to which the latter were subjected. 



DEVONIAN ROCKS OF SOUTH DEVON 



The Devonian rocks of south Devon consist mainly of argillaceous 

 sediments. These are associated in the Lower Devonian with more or 

 less fine grained grits and silty rocks in very variable proportion. The 

 Middle Devonian succession varies in different districts and in different 



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