176 



Feet. 



Height of the dome above the horizontal plane 430 



Depth of a shaft from this plane to the first dotted 



lino = 7 miles x tan. 10° 6,517 



Breadth of the Ludlow and Wenlock series 2,384 



9,331 

 This calculation must be taken only for what it is intended to be, an 

 approximation to the truth, to which future con-ectiona may be applied. 



A graphic description of a similar result of volcanic action, curiously 

 approaching accuracy in an age not renowned for physical science, may be found 

 in Ovid's account of a mountain in the plain of Trsezen. (Metam. xv. 296 — 

 306). 



DENUDATION. 



Under this head are comprehended the various marine fluviatile and 

 pluvial influences, which have combined to strip off the isolated fragments of 

 the beds, to erode the soft shales into concentric valleys, and to enlarge the 

 fractures and dislocations. If we could imagine the strata replaced in their 

 positions on the dotted lines in fig. 2, tons upon tons of rock would be required 

 to fill up the gap. I once made a calculation of the weight of rocks actually 

 removed, but I have not produced it now, because its many unsafe assump- 

 tions and general roughness rendered it of little value. Now it is with reference 

 to the process of such denudation that the two rival schools of geologists mainly 

 differ; the one, of which Sir C. Lyell is the acknowledged head, maintaining 

 that causes now existing are competent to produce all the phenomena which 

 Geology exhibits to us, that if sufficient time is granted, we need not seek any 

 additional cause or any unusual intensity. It is well known that in the S.E. 

 of England there is a magnificent valley of elevation called the ^yeald, of which 

 our own valley is a copy in miniature. The parallelism between the beds of 

 the two valleys is as follows : 



WOOLHOPE. 



Upper Ludlow and Aymestry rocks 

 Lower Ludlow 

 Wenlock Limestone 

 Wenlock Shale 



Woolhope Beds and Upper Llandovery 

 Sandstone 



Weald. 

 Chalk and Upper Greensand 

 Gault 



Lower Greensand 

 Weald Clay 



Hastings Sands with some proti-usions 

 of lower beds 



Any one who wishes for more complete information on Sir C. Lyell's 

 views on this subject may refer to the ''Elements", chap, xix., where the 

 denudation of the Weald is discussed ; and this chapter mutatis mutandis 

 may be held to convey his ideas on the denudation of the Woolhope valley. 

 The other school, which numbers in its ranks the majority of the older geolo- 

 gists, although not unwilling to allow abundance of time, yet puts forward a 

 claim for greater intensity of causation, paroxysmal violence, catasti-ophes and 

 convulsions of nature. In the eloquent 20th chapter of the now edition of 

 "SUuria," the most resolute and earnest opponent of the uniformitarian theory 

 expresses his views on the subject of denudation, seleoting om own district as 



