168 J. R. Dakyns — Sediment Theory of Drift. 



outcrop must necessarily be conjectural. A large east and west 

 fault, between Wiveliscombe and Bishops Lydeard, throws all the 

 beds north of it, further east ; so that Sandstones and Breccias of the 

 lowest division are faulted against Upper Sandstones ; Lower Marls 

 entirely eliminated ; Conglomerates and Upper Sandstones faulted 

 against Upper Marls. The frequency of these disturbances renders 

 estimates of the thicknesses of the beds, even in the Coast Section, 

 extremely conjectural. 



TJiicTcness. 

 In taking estimates from the Coast Section, the fault at Seaton ; 

 synclinal structure at Beer; fault at Chit Bock, throwing down 

 Upper Marls, West of Sidmouth ; faults near Lardrum Bay repeating 

 bottom beds of Upper Marls ; numerous faults affecting Lower Marls 

 and Lower Sandstones, between Straight Point and Exmouth, 1 and the 

 elimination of a part of the lowest division at the latter place ; faults 

 in the breccia between Dawlish and Torquay ; and a considerable 

 allowance for the fact that the coast-line, between Exmouth and 

 Torquay, is diagonally across the dip, and therefore does not show the 

 breadth of outcrop ; must be taken into account. We have not yet 

 finished the re-survey of these rocks, so that our estimates of their 

 thickness, particularly of that of the Lower Marls and underlying 

 beds, must be taken as problematical, not, however, erring on the 

 side of parsimony. There is no apparent foundation for the miles of 

 thickness that have been ascribed to them, and Sir H. de la Beche 

 seems to have formed a shrewd estimate, which, though possibly 

 under the mark, is some miles nearer than the more liberal calcula- 

 tions. Judging from what we have seen, Mr. Woodward agrees with 

 me in considering that the following estimates do not err on the side 

 of limitation. 



1. Upper Marls (of Coast Section) 1,000 feet. 



2. Upper Sandstones 460 „ 



3. Conglomerates and Pebble-beds 80 „ 



4. Lower Marls 460 „ 



5. Lower Sandstones and Breccias 1,000 „ 



3,000 „ 



IV. — The Sediment Theory of Drift. 



By J. E. Dakyns, M.A., 



Of the Geological Survey of England and "Wales. 



THE publication in the Number of the Geological Magazine for 

 November, 1874, of Mr. Goodchild's ingenious Drift theory 

 leads me to make a few remarks on the subject. 



1 Since the above was written, Mr. P. O. Hutchinson, of Sidmouth, kindly furnished 

 me with a sketch section of the railway cutting between Langsant Point and Dawlish, 

 made during a visit to the latter place, and showing, besides numerous small faults, 

 one of considerable importance, on the west side of Langsant Point ; as the Breccia 

 occurring at that Point and in the plantation at Exmouth is almost exactly similar to 

 that exposed in the cliffs, by the beach, on the west of Dawlish, and the beds in the 

 railway cutting chiefly consist of sands, the probability of these latter being repre- 

 sentatives of a part of the sandstones of the division No. 5, cut out by the fault at 

 Exmouth, immediately struck me. Future investigation will probably supply the 

 solution, which, if my inference be correct, would lead to a further reduction in the 

 estimation of the thickness of division No. 5. 



