Yol. 62.] LIMESTONE OF THE MENDIP AREA. 337 



strictly speaking, with reference to four periclines, each of which 

 has its longer axis trending approximately east and west. 

 Denudation of the summits of these periclines has exposed the Old 

 Red Sandstone at Black Down, North Hill, Pen Hill, and Beacon 

 Hill (see map, PI. XXXIII). Taken in order south-eastward, these 

 periclines are as follows : — 



(1) The Black-Down pericline, extending from near Compton Martin west- 



ward, through Black Down and Bleadon Hill to Brean Down, and 

 finally represented, in mid-channel, by the Steep Holme. 



(2) The North-Hill pericline, extending westward from Red Hill (near 



Emborough) through Eaker Hill and North Hill to Priddy, and still 

 farther westward from Priddy, towards Draycott. 



(3) The much-faulted pericline of Pen Hill, which extends, in a direction a 



little south of west, from Grurney Slade and Binegar to Pen Hill and 

 Rookham Hill, and probably affects the ground north of the Ebbor 

 Valley, considerably west of Rookhain Hill. 



(4) The Beacon-Hill pericline, extending eastward from Maesbury, through 



Beacon Hill, Tadhill and Little Elm, to the vicinity of Frome. 



In addition to these main folds, other minor folds and many 

 faults have affected the structure of the area. The east-and-west 

 anticline of Tor Hill and Lyatt Hill, south of the main outcrop, is 

 probably connected with the anticline which, according to the 

 Geological Survey-memoir, 1 is indicated near Bowlish, immediately 

 north of Shepton Mallet. 



The existence of so many isolated masses of Carboniferous 

 Limestone, south of the main outcrop, as at Nyland Hill, Lodge 

 Hill, Wookey, Dulcote Hill, Worminster, etc., points to considerable 

 disturbance, probably of a complex nature. 



The important faults and fault-complexes of the Mendips are 

 mainly confined to the eastern half of the area. The following are 

 some of the most noteworthy : — 



(1) The great thrust-fault on the south side of the Ebbor Valley, south of 



Priddy, which has thrown beds of the Upper Za}ihrentis-Zone against 

 shales of ' Millstone-Grit ' age. 



(2) The extensive fault, or system of faults, on the north side of the Old 



Red Sandstone of Pen Hill. 



(3) The fault-complex of the Emborough district. 



(4) The great north-and-south fault of Heale and Downhead, on the south 



side of the Beacon-Hill pericline, which has let down the beds on the 

 east, and thus considerably reduced the width of the Old-Red-Sandstone 

 outcrop north of Downhead and at Little Elm. 



(5) The complex movements which have produced inliers of Carboniferous 

 Limestone at Vobster and Luckington, in the Radstock Coalfield, north 

 of the Mendip outcrop. 



The outcrop of the uppermost part of the Avonian Series, in the 

 Mendip area, is very limited in extent, and is chiefly confined to 

 the district between Gurney Slade, on the west, and Mells, on the 

 east, bordering the northern outcrop of the Millstone Grit. This 

 is due to : — (1) The enormous amount of denudation which the 

 district has suffered in various periods ; and (2) the incomplete 



1 ' Geology of East Somerset & the Bristol Coalfields' 1876, p. 196. 



