15 



absent in South Wales, it is only in certain places that these subdi- 

 visions can be defined. In addition to this, the several formations 

 thin out so rapidly in their course to the south-west, that beyond 

 Llandeilo, the Ludlow and Wenlock formations appear in the same 

 escarpment, and in like manner on the left bank of the Towey, be- 

 tween Llandeilo and Llangadock, it is difficult to separate the shelly 

 sandstones of the third formation from the black flags of Llandeilo, 

 with which they are associated ; the great fossiliferous system which 

 in Shropshire, Hereford, Radnor, &c. is expanded over so wide an 

 area, being there compressed into a narrow zone between the old 

 red sandstone on the one side and the rocks of roofing slate on the 

 other. 



II. The next chapter describes such of the above-mentioned for- 

 mations as occur in the Abberley Hills, upon the flanks of the Mal- 

 vern Hills, Herefordshire, in the vicinity of Usk, Monmouthshire, 

 or in May and Huntley Hills, Gloucestershire, &c. It is stated that 

 Nos. 1 and 2, or the Ludlow and Wenlock formations, are much the 

 most persistent, usually occupying two distinct ridges, as in Shrop- 

 shire, though on a smaller scale. The impure limestone at the base 

 of the Wenlock shale and constituting the top of the shelly sand- 

 stones is also strongly marked by its peculiar characters and organic 

 remains. The arenaceous or great mass of this third formation is 

 brought out from beneath the others at certain points only, as at 

 Ankerdine and Old Storridge Hills, and at Howlers Heath, Wor- 

 cestershire. May Hill, in Gloucestershire, is cited as a good type 

 of the formation, where it is also overlaid by the superior deposits. 



III. Woolhope Valley of Elevation. — A valley of elevation which 

 the author conceives to be the most symmetrical in Great Britain, 

 is then pointed out as occurring south-east of Hereford, where the 

 two superior formations of the grauwacke series are incurvated 

 round a central dome-shaped mass, composed of the shelly sand- 

 stones of the third formation, from which the strata dip away on all 

 sides at angles varying from 15° to 70°. The harder strata of each 

 formation having resisted destruction, whilst the shales have been 

 worn away, the former constitute the higher encircling ridges, the 

 latter deep trenches of intervallation. The outer zone contains all 

 the fossils characteristic of the Ludlow rocks, and passes beneath 

 the old red sandstone; the inner zone, those of the coralline forma- 

 tion of Wenlock and Dudley, and both these are wrapped round 

 a nucleus of the third formation. The outer zone is unbroken by 

 any transverse gorge, throughout two thirds of its circumference ; 

 but at Mordiford it is violently dislocated, and the result has been 

 a chasm, by which and by two minor fissures, the valley is en- 

 tirely drained. The whole of the valley is stated to be one of clean 

 denudation, being entirely free from any fragments, even of the old 

 red sandstone, though the inferior and denuded strata must have 

 been raised up through that formation. The author calls atten- 

 tion to the south-eastern apex of this valley, where the encircling 

 formations successively become confluent, and the line of the 

 axis of elevation in its prolongation to the south-east being alone 



