486 



THE WREN'S NEST— DUDLEY. 



The solid strata of limestone have not, however, been thus raised and incurvated 

 around a common centre without transverse breaks. In addition to the fissure along 

 the axis of the ridge, there is a fracture of considerable magnitude at the south-south- 

 eastern turn of the ellipsoid (see ground plan), and precisely at that point where the 

 appearance of symmetrical curvature of the mass is preserved. Here, the outer band 

 of limestone sweeps round in the wide arch, represented in the previous page, the ex- 

 ternal part of which (towards the south and south-west) is most expanded, owing to 

 the less inclination of the beds. As these strata approach the south-eastern turn, they 

 rise rapidly in inclination, and seem, on a first view, to be continuous from that point 

 along the eastern face. But this appearance is entirely fallacious j for the outer band 

 is there brought into exact allinement with the inner; i. e. the trench of circumvallation 

 from which the one limestone has been extracted, seems to be a continuation of the other. 

 On closer examination the anomaly is explained. The inner or lower limestone having 

 been subjected to a very high degree of flexure, has been snapped asunder close to the 

 farm-house of the Wren's Nest (o), where the quarries expose great tortion and fracture. 

 By this dislocation, the inner limestone is entirely lost, its place being occupied by shale 

 and bavin. The same stratum, however, on the eastern face, becomes vertical opposite 

 the great cross fracture, and although at one point coincident with the outer band, it 

 does not fold round to the west, but continues its strike to the south and by east, in 

 which direction it has been quarried at a spot called Gabriel's Hole, and has been also 

 cut through by the tunnel of the Dudley canal. 



If the Wren's Nest, judging from its hollow axis, be termed a valley of elevation, its 

 size and sharply confluent flanks, as well as the materials of which it is composed, have 

 led to peculiar modifications of form, very different, for example, from those of the 

 Valley of Woolhope (p. 428.). The central mass of the latter being of wider area and 

 only slightly curved has not been fractured, and, further, being composed of hard 

 grit has resisted denudation and still remains a dome. (PI. 36. f. 9.) In the Wren's 

 Nest, on the contrary, the limestone, which doubtless must once have capped its 

 centre, has (owing to the sharp convolution to which it was subjected) been snapped 

 asunder and removed, and thus the soft shale being exposed to denuding influences, a 

 cup-shaped centre has resulted. In this respect, indeed, the Wren's Nest resembles 

 the Valley of Wigmore near Ludlow, where the exposure of the same soft shale has led 

 to a similar, but much deeper denudation. In pursuing the parallel with Woolhope, 

 the reader will bear in mind, that there, the surrounding trenches are those of nature, 

 the perishable strata having been denudated and the solid stone forming banks ; whilst 

 in the Wren's Nest the trenches are the work of man, and have been fashioned out of 

 the hardest materials in the hill. We shall hereafter consider the probable cause of 

 the ellipsoidal form of this and the adjacent masses of limestone. 



