GEOLOGY 



schist, knoten glimmerschiefer, actinolite hornfels and actinolite schist, 

 with a dyke (gang), several metres in thickness, of garnet rock with 

 actinolite and axinite. 



Variously claimed as a post-carboniferous plutonic intrusion, a Per- 

 mian volcano,' an upthrust in the period before the deposition of the 

 Middle Culm,* or as an ancient granite' modified amongst its surround- 

 ings at a comparatively late stage in the post-carboniferous movements 

 (during a rise in the isogeotherms accompanied by the injection of elvan 

 dykes), the Dartmoor granite, owing to its size and shape and the mani- 

 fest effect its presence has had on the strikes and distribution of the 

 surrounding rocks, remains the sphinx of Devon geology. 



NEW RED SANDSTONE SERIES 



The coast section exhibits numerous faults in the New Red rocks ; 

 these in the Lower breccias are often accompanied by high dips which 

 become lower toward the east. In inland districts faults can only be 

 traced by the displacement of lithologically distinguishable horizons. 



The Lower New Red rocks show a remarkable attenuation toward 

 Exeter, and further north their development is exceedingly irregular ; 

 in rounding the spurs or inliers of the Culm rocks (at Pinhoe, Spray- 

 downs near CoUumpton, at Westleigh and Whipcots) being so feeble and 

 inadequate as to suggest either a faulted or unconformable junction with 

 the overlying Marls, rather than the outward replacement of coarser by 

 finer sediment. 



Watcombe Clays. — These consist of red rather silty finely micaceous 

 clays or marls, with intercalated beds of comminuted slate in the lower 

 part, exposed in Petitor Combe, and overlain by about 20 feet of similar 

 material occasionally showing annelid tracks, where they pass under the 

 conglomerates in Watcombe Combe. These clays lose their distinctive 

 characters, becoming a loamy or clayey breccia, when traced inland. 

 Their thickness on the coast may be about 150 feet. 



Watcombe Conglomerate. — These beds are typically exposed in Wat- 

 combe and Petitor Crags. They are characterized by large well worn 

 fragments of Devonian limestones associated with grit, quartz, and some 

 igneous materials in a sandy matrix. Contemporaneous erosion is shown 

 in them in Oddicombe Cliffs, where they contain thick beds of sand. If 

 these rocks extend north of the Teign estuary they are represented by 

 sand or sandstone about 20 or 30 feet thick at Bishopsteignton. On the 

 coast they can scarcely be less than 500 feet. They seem to be lower in 

 the series than the earliest evidences of contemporaneous trap. They 

 pass under the next series at Mincombe and form the base of the cliff at 

 the Ness. 



T'eignmouth or Boulder Breccias. — These beds form a brecciated and 

 boulder-studded red sandy loam. The boulders are chiefly of quartz- 



1 Worth, Trans. Plymouth Instit. (1888-9). 



* Somervail, Report Brit. Assoc. Bristol (1898) and Geol. Mag. (Dec. 4), vol. v. p. 509. 

 ' Proc. Somerset Arch. etc. (1892), vol. xxxviii. 



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