TSIASSIC STRATA OE THE SOUTH-WESTERN COUNTIES. 467 



to have been often contemporaneously formed (as near Collumpton 

 and Tiverton, &c). 



(/) It now remains to consider the Basement-beds in their in- 

 ternal relations. On the sonth coast they are much disturbed by 

 faults, which can seldom be laid down in inland localities, owing to 

 the changeable nature of the division. 



Taking the sands cut out at Exmouth as 100 feet in thickness, 

 which, judging from their development between Honiton's Clist and 

 Topsham, does not appear to be excessive, we might regard the beds 

 represented between Langstone Point and Dawlish * as a passage- 

 series into breccia. For this passage-series, which appears to ter- 

 minate at the mouth of the tunnel at Dawlish (though repeated in 

 several places towards the Clerk Rock by faults), 150 feet cannot 

 be regarded as an excessive thickness. The subjacent breccia is much 

 faulted, but appears to belong to the same horizon in the division, 

 from its outcrop to Watcombe, where the breccio-conglomerates with 

 limestone pebbles crop out on the top of the cliffs. It may be re- 

 garded, with due allowance for repetition by faults, as at least 500 

 feet in thickness, as the cliffs composed of it sometimes exceed 350 

 feet in height. 



The limestone conglomerate of Watcombe may be regarded as 

 affording a further thickness of 400 feet; and the local series of 

 basement clays and sands of Petitor and Watcombe may be taken 

 as 100 feet. 



If the Paignton beds are of earlier date, an addition of from 150 to 

 200 feet would have to be made ; but I regard them as the equiva- 

 lents of the basement-beds to the north of Babbicombe, and their 

 difference in character as due to local sources of derivation. 



(g) Upon the foregoing determination the mean and maximum 

 thicknesses of the South-Devon basement-beds, divided into three 

 horizons, each passing into the other by intercalation, would be as 

 follows : — 



Mean. Maximum, 

 feet. feet. 



1. Sandstones and passage-sands and breccias ... 250 to 400 



2. Rubbly breccia with igneous boulders 500 ,, 600 



3. Conglomerate and breccia with numerous lime- 



stone fragments 400 „ 500 



4. Watcombe and Petitor sands and clays 100 „ 150 



Total thickness from 1250 to 1650 



When traced inland we find a very great attenuation of this divi- 

 sion, and that the variability of its constituents precludes the settle- 

 ment of any definite general horizons. Thus, north of Exeter, the 

 whole superficial portion of the division is represented by sands and 

 sandstones (fissile near Broad Clist) with occasional clayey beds ; yet, 

 from the subjacent position of the breccia of the Crediton valley, it 



* The Langstone-Point and Exmouth breccias are regarded as portions of 

 the subjacent series thrust up by faults. 



