SUBTERRANEAN CONE OF TRAP. 



129 



twenty-two yards had widened considerably, it was proved to be a mass of conical shape 

 rising up through the strata of the coal-field. 2ndly. When quarried underground this 

 singular mass was tolerably hard, but on exposure it became quite soft, crumbling into 

 a number of small round sub-conchoidal lumps. 3rdly. The composition of this rock 

 as well as its intrusive characters proved it to be of igneous origin. The base contains 

 much silex and some peroxide of iron, with disseminated crystals of felspar, and it acts 

 slightly on the needle. It must be considered as belonging to what has been called 

 " trap wacke " by mineralogists. The strata on the eastern or coal-field side of this in- 

 truder consisted of broken chinch, and also of a detached and highly dislocated band of 

 grit thrown quite across the other beds described. (PI, 30. fig. 8. a # .) 



Further to ascertain the condition of the ground, Mr. Lewis continued his lower drift horizontally 

 towards the basaltic cap of the Hoar Edge for the length of fifty-two yards from the vertical shaft, 

 carrying it along under the bottom coal rock; and throughout this trial the measures proved to be 

 very regular, little faulted, and dipped at slight angles to the south-east or towards the centre of 

 the basin. This examination, therefore, leads very naturally to the inference, that as the measures 

 approach the centre of the coal-field, the coal may expand, and that Mr. Lewis may one day be 

 rewarded by finding all the other coal seams as regularly in their places beneath the sheet of basalt 

 at the Hoar Edge, viz., on the western side of the Jewstone dyke, as in the great works of Corn- 

 brook before described. (See Map and diagrams, PL 30.) There can, indeed, exist no good reason 

 why the coal should not be as largely developed on the one side of the great Jewstone dyke as on 

 the other. 



Theoretically, the discovery of the conical mass of trap is of deep interest in explaining 

 the method by which the sedimentary deposits of these hills have been so powerfully 

 disturbed. It was certainly a most happy accident for the geologist, that this coal shaft 

 should have been sunk precisely above the narrow apex of a cone of this rock, and we 

 are greatly indebted to Mr. Lewis, both for continuing his sinking to a depth of nearly 

 seventy feet in this mass, and for his successful endeavours to regain the coal seams, in 

 doing which he determined the form of the intruder. This cone of trap may be sup- 

 posed to have been the result of an effort towards eruption, which though not reaching 

 to the surface, has produced many of the effects common to such intrusions, whilst the 

 chief source of eruption has been the great jewstone fault, through which all the pure 

 basaltic matter has been ejected, and which reaching the surface has overflowed the 

 principal coal-field in the manner before explained. 



Basalt of the Broivn Clee Hill. — The lithological structure of the basalt of the Brown 

 Clee is, as already stated, in every respect identical with that of the Titterstone Clee, and 

 crowning the summits of the Abdon and Clee Hill Barfs, it also overlies the carboniferous 

 strata in the latter hill. We have not here the same clear proofs of a channel of eruption 

 as in the Titterstone Clee, but from the evidence of some of the oldest workmen, there 

 is every reason to think that the basalt of the Abdon Barf, or the highest point, forms 

 a solid and unfathomable mass, particularly at the northern end. In all other parts of 



