TRIASSIC STRATA OP THE SOUTH-WESTERN COUNTIES. 461 



subjacent to the conglomerate division) seldom attains to 800 

 feet in the Burlescombe district, and in the neighbourhood of 

 Wiveliscombe and Stogumber : in the districts embracing the val- 

 leys of Tiverton and Crediton it probably exceeds 1000 feet ; but on 

 the south coast a maximum development of 1650 feet might be con- 

 ceded to it. From this it seems probable that a still greater de- 

 velopment may have been attained in the area now occupied by the 

 English Channel. 



(/) The gradual replacement of the foreign quartzites of the 

 Budleigh-Salterton pebble-beds by material capable of local deriva- 

 tion as the beds are traced northwards, indicates the existence of 

 currents from the south during the early stages of the Keuper 

 period. 



My friend Mr. Linford, of Exeter, has devoted much time to the 

 investigation of the origin of the Budleigh-Salterton quartzite- 

 pebbles. After several visits to Normandy, he came to the conclusion 

 that the pebbles were drifted by northerly currents and obtained 

 from a previous extension of the quartzites of Calvados and La 

 Manche * into the area now occupied by the English Channel (vide 

 Eep. and Proc. of the Tamworth Nat.-Hist., Geol., and Antiq. Soc. 

 vol. i. part 1, p. 41, &c). Mr. Linford also visited Tamworth and 

 Bromsgrove, in which localities he observed pebbles lithologically 

 similar to the characteristic Budleigh pebbles (Comp. Brodie, Quart. 

 Journ. Geol. Soc. vol. xxiii. p. 211, &c.) in drifts, and traced them 

 to Triassic conglomerates in their respective vicinities. 



Eifth proposition. — That, from the presence of numerous frag- 

 ments of igneous rocks (quartz porphyries) in the basement beds of 

 the South-Devon Trias, and from the absence of any known rocks 

 in the county to which they could be readily referred, it appears 

 probable that the cliffs and bed of the early Triassic sea were partly 

 composed of igneous rocks of similar character to the foreign fragments. 

 That any portions of such rocks left undestroyed would be likely to 

 occur (1) under the Triassic beds in the vicinity of Dartmoor, (2) 

 concealed by the Trias between Newton Abbot and Seaton, or (3) in 

 the area now occupied by the English Channel. 



The proof of this proposition is combined with its enunciation. 

 My friend Mr. Vicaryf has long been of opinion that the igneous 

 fragments are directly referable to varieties of the Dartmoor granites, 

 having visited many localities in Dartmoor where the granite 

 is so similar in character to these porphyritic fragments J that 

 nothing but a change in colour is wanting to complete the resem- 

 blance. Mr. Yicary succeeded in producing the change in colour by 

 heating specimens of Dartmoor granite. Though there is no reason 

 to suppose that the partially consolidated breccias in which the 



* The Norman origin of the pebbles was first advocated by Mr. Salter, Quart. 

 Journ. G-eol. Soc. vol. xx. p. 287. Geol. Mag. vol. i. 1864, pp. 5, &c. 



t Trans. Dev. Assoc, for 1867, vol. ii. p. 200. 



t Decomposed flakes of mica are frequent in these fragments, quartz por- 

 phyries according to Prof. Judd. See a paper by Mr. T. Andrew, Trans. Dev. 

 Assoc, for 1870. 



