ROCKS OF SOMERSET AND DEVON". 381 



Extent. — With one exception south of Williton, where these beds 

 are faulted out, they run with an average breadth of outcrop of 1| 

 mile, between Williton and Otterton Point, a distance of over 30 

 miles : in sheet 22 of the Ordnance map, north of Otterton Point 

 their breath of outcrop appears to be from 3 to 4 miles ; but this is 

 probably due to repetition by faults. 



Economic Uses. — At "Watt's Bridge, near Bishops Lydeard, some 

 hard thick-bedded sandstones, used for building-purposes, occur in 

 this division. Between Bishops Lydeard and Crowcombe the 

 calcareous sandstones are largely quarried to burn for lime. 



Thickness. — In estimating the thickness of these beds we cannot 

 allow more than a mile and a half of outcrop, north of Ottery St. 

 Mary, which, with a dip of 3° persistent, would give a thickness 

 of about 400 feet. If we take the coast section, it is plain that an 

 estimate made at right angles to the strike, measuring outcrop from 

 their junction with the last capping of marl (supposing the absence 

 of disturbances) to the outcrop of the pebble-beds of Budleigh 

 Salterton, would give the true thickness. 



Estimates have been previously made ignoring any disturbances 

 in these rocks as displayed on the South-Devon coast, on the ground 

 that the beds cut out by faults, would balance those repeated : a 

 glance at the section of these sandstones made from close observa- 

 tion of the coast will, at least as far as this division is concerned, 

 show the fallacy of this reasoning. The fault at Chit Bock brings 

 down about 200 or 300 feet of Upper Marls — the same sandstones 

 there cut off appearing again at the base of the cliff south of Peak 

 House, and again outcropping on the surface south of High Peak, 

 but not finally, as a fault with a downthrow of about 50 feet again 

 brings down Upper Marl a little to the north of the Preventive 

 Station at Ladram Bay. About 80 yards further south the first 

 cutting-out fault occurs, which disposes of about 5 feet of marl ; 

 but this is more than counteracted by another fault not 80 yards 

 further south, which throws down about 14 feet of marl, the sand- 

 stone finally emerging from the last capping half a mile south of the 

 road to the beach, at Ladram. Even from this point we cannot 

 take the coast section, as it frequently represents the strike of the 

 beds, and in many places they appear perfectly horizontal, whilst 

 in one place, as may be seen in the section, either a fault or a 

 crack (I have not yet succeeded in ascertaining which) by inland 

 evidence occurs. So, allowing the coast-section sandstones an out- 

 crop of 2| miles, and a persistent dip of 2°, we have a thickness of 

 about 530 feet — if any thing, an excessive estimate. 



Both from a better acquaintance with these beds as shown on 

 the coast, and to point out a few of the difficulties in the way of 

 estimating the thickness of the divisions, even where the relations 

 between the under and overlying members are observable, I have 

 gone into their occurrence in the coast sections at greater length. 



The traces of conglomerate at Otterton Point may be considered 

 indicative of a passage into the next series — ■ 



