A HISTORY OF DEVONSHIRE 



porphyry (of a type hitherto only met with near Christow on the border 

 of Dartmoor). The stones include a great variety of altered and igneous 

 rocks. The quartz-porphyry boulders are sometimes almost unworn and 

 so large that they must have been derived from rocks in their immediate 

 vicinity. These rubbly breccias locally contain harder beds of breccia or 

 breccio-conglomerate with limestone pebbles, In 1887 a boring for 

 water at Combe, near Teignmouth, was carried to a depth of 332 feet in 

 them. They overlie the trap (quartz basalt) patches of Dunchideock, 

 Knowl and Westown. 



Dawlish Breccia and Sands. — At Holcombe Tunnel the rubbly 

 Boulder Breccias are succeeded by the Dawlish Breccias — the Murchi- 

 sonite beds of Ormerod — beds of sand-rock thickly studded with rather 

 small fragments of altered and igneous rocks and murchisonite, with 

 occasional coarser bands of breccia. The breccias of the Crediton valley 

 are of this type. These rocks contain intercalations of sandstone and 

 vary from sand to breccia most irregularly along the coast from Dawlish 

 to Exmouth. The materials become differentiated toward Exeter and 

 form an upper series of sands at Topsham, upon the Heavitree breccias, 

 the basement beds being brecciated loam and sand, which overlie the 

 trap rocks of Pocombe and Northernhay. The sands of Broadclist and 

 Poltimore seem to be the upper beds of the series, and there are several 

 patches of trap associated with them.' 



With the narrowing of the Crediton valley at Newton St. Cyres 

 the sands give place to breccia full of igneous fragments, which overlies 

 the trap patches of Posbury, Halse and Greenslade on the south, and of 

 Knowle and Spencecombe on the north side of the valley. These trap 

 patches rest on sand and breccia, which on the north side of the valley 

 seems to be largely formed of tuifs. A similar phenomenon is observ- 

 able under the Washfield traps. 



The gravelly breccias occur over sands in the Spraydown Culm 

 inlier, and are found to pass from the Culm highlands irregularly out- 

 ward into sand, often through breccia or brecciated sands. They contain 

 fossiliferous stones {Strophalosia caperata, Rhynchonella pleurodon), from the 

 Upper Devonian area on the north, in the railway cuttings of the Exe 

 valley line north of Tiverton.^ The Rev. W. Downes attributed these 

 stones to volcanic ejectamenta, and pointed out the presence of fragments 

 referable to the Washfield traps in the cuttings near Bolham. At Cole- 

 ford Lodge near the margin of the Stoodleigh Beacon outlier a small 

 patch of trap seems to rest on the gravel. The Upper Devonian fragments, 

 also found in the gravels near Cadbury, Uplowman and Silverton, point to 

 the explanation given in the introductory notes (see p. 5). The Halber- 

 ton breccias seem to be the upper beds of the Lower New Red in that 

 neighbourhood. The strikes of the Lower New Red rocks, as might be 

 expected from the trend of the creeks, etc., in the older rocks, are more 



' For relations and petrology of trap rocks, see Geol. Survey Memoir on the country around Exeter 

 (1902), chap. iv. 



* Downes, Trans. Devon Assoc, for 1881, pp. 293-7. 



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