392 W. A. E. TJSSHER ON THE TRIASSIC 



as at Stoodleigh Beacon and Spray Down, and the rough parallelism to 

 the old rock-margin exhibited by the majority of the faults affecting 

 the Trias seem to lead to the conclusion that a partial upheaval, at 

 least, of the rocks on which the Lower Division of the Trias rests, in 

 Post-Triassic times gave their easterly tilt to the Secondary Rocks, 

 and probably aided in producing the folds observable in the Culm- 

 limestones of West Leigh and its vicinity. 



To what extent the Triassic beds may have suffered from denu- 

 ding forces since that elevation, and how far the upheaval of the 

 older rocks has been Post-Triassic, is a question upon which future 

 investigations and careful survey will probably throw some light. 

 The existence of gravel patches upon the older rocks, near the 

 margin of the Triassic area, in some districts, the fact that material 

 for the formation of such gravels would be readily furnished by the 

 disintegration of certain varieties of breccia of the Lowest Triassic 

 division *, the fact that this gravel actually overlies and is hardly 

 separable from an outlying patch of brecciated sand near Stoodleigh 

 Beacon, 6 miles north-west of Tiverton, and isolated by nearly 2 

 miles of Culm-measure shales and grits from the main mass of the 

 Trias, and the careful indication of three minute patches of sandstone 

 (probably of the lower series) on the top of Grabbist Hill near 

 Minehead, by my friend and colleague Mr. Blake, all lead to the 

 inference of a very much greater extension of the Devonshire and 

 "West Somerset Triassic rocks before the upheaval which (probably 

 successively ?) exposed them to denuding forces, and, leaving but 

 very few traces as beacons of their former site, afforded by their 

 destruction plentiful material for the formation of subaerial gravels 

 and thick soils. 



Thickness f. 



Summing up the outside and very problematical estimates want 

 of better compel me to offer, we have for — 



Upper Marls 1350 



Upper Sandstone 530 



Conglomerates 100 



Lower Marls 600 



Lower Sandstone and Breccia .... 1000 



3580 feet in all, 

 though 2500 feet appears a more likely estimate. 



* Some of these outlying patches of High-Level Gravel have been visited 

 since the abov^e had gone to press ; and I do not now entertain a doubt as to 

 their Triassic age. 



t The different amount of the dips allowed in forming estimates of the 

 thickness of each division would at first sight appear anomalous in a conform- 

 able series of beds ; but when the different localities from which the estimates 

 have been made, and the local variations so commonly experienced in the 

 occurrence of the divisions, are taken into account, the difficulty of obtaining 

 results from one locality alone will be appreciated. 



