ROCKS OF SOMERSET AND DEVON. 391 



Assuming the rocks north of this axis to be unfaulted, the few dips I 

 have taken in them, averaging 10° due south, must not be taken into 

 account, as they are only local ; and any estimate before the whole 

 valley is resurveyed and a more minute examination made of the 

 part already gone over, would be premature. 



The Tiverton valley, with a breadth of 4 miles north and south 

 through Halberton, seems also to present a synclinal in these beds. 



If we allow a tolerably persistent thickness for the Lower Division 

 over the whole area, which is very unlikely, the Watchet district 

 might afford a clue. ■ Assuming that their average width, about a 

 mile (south of Stogumber), is a persistent outcrop where the whole 

 thickness of the division is represented, a persistent dip of 8° would 

 give a thickness of about 720 feet. Allowing the coast-section beds 

 to represent a maximum development, Mr. Woodward agrees with 

 me in considering 1000 feet as an outside estimate for them. 



General Observations. 



In the foregoing all the estimates made of the thickness of the 

 divisions must be considered merely approximations based upon 

 such material as the survey of most of the district has supplied me 

 with. Tracts yet remain to be investigated which will probably 

 throw more light upon the relations of two of the divisions— the 

 Pebble-beds and the Lowest Division. 



Mr. H. B. Woodward has subdivided the Triassic rocks in the 

 immediate neighbourhood of Williton, and in that district fully 

 corroborated the sequence of which it is the object of this paper to 

 attempt a description. As previously stated, I do not insist that 

 this sequence is present over the whole area covered by Triassic 

 rocks in West Somerset and Devon, or even over a much greater 

 space than where it is exposed. 



In a slowly and unequally subsiding area beds of breccia may 

 have been forming before the land under the area now covered by 

 the Upper Marls -had come within the influence of the destructive 

 and accumulating agencies at work in other portions of the district ; 

 and, when it did, the sediment deposited may have been of a 

 totally different character. I only desire to show that, from the 

 outcrop of the Upper Sandstones to the older rock-margin, this 

 sequence, considering the impersistent nature of the divisions, is, 

 we might almost say, abnormally persistent. 



At Exeter, about Silverton and south of it, in the Crediton valley, 

 and at the western extremity of the Tiverton valley, patches of 

 basalt occur in connexion with the Lowest Division. Their mode 

 of occurrence and composition will be treated of in the Geological- 

 Survey memoir. 



The frequent high dips exhibited by the lower beds of the Trias 

 down the slopes of the older rocks, upon which they rest, decreasing 

 in amount of inclination, though generally persistent in direction as 

 we recede from their (the older rocks') superficial limits, the presence 

 of patches of the lower beds of the Trias on the Palaeozoic Highlands, 



