450 J. PrestwicHj Esq.^ on the 



fine grained, hard, dark, dull-looking porphyritic greenstone, in some places 

 slightly amygdaloidal, and traversed by parallel divisional planes. It has the ap- 

 pearance of having been tilted at angles of 50 or 60 degrees, by the interior 

 nuclei, an arrangement which suggests the subsequent protrusion of the 

 eurite; and from the manner in which the quartzose grits are connected with 

 the greenstone, I am induced to consider the latter as one of those numerous 

 igneous rocks, which are interstratified with the lower Silurian formations. 



To the east of this main axis and parallel to it is a small ridge of dark, very 

 compact greenstone (see Map, Plate XXXVI.). Another extensive outcrop 

 of igneous rocks ranges S.S. W. and N.N.E. from the " Spout" to Steeraways. 

 It consists of a fine-grained greenstone^ generally syenitic and sometimes 

 amygdaloidal, with siliceous and ferruginous concretions. This ridge has 

 evidently been protruded, as it tilts the limestone eastward at a high angle. 

 There generally occurs*, between the carboniferous series and the green- 

 stone, a dark, hard basalt, passing into wacke, sometimes of a dirty yellow co- 

 lour and a soft earthy texture; more frequently, however, of a dark liver-red, 

 occasionally fragmentary and hard, with a lustrous surface, but oftener friable 

 and clayey ; in some places it is amygdaloidal, with concretions of phrenite and 

 oxide of iron. This superposition is observable at the Hatch (seePl.XXXVIL, 

 fig. 6.), and around Little Wenlock, where the dip of the trap conforms to 

 that of the carboniferous limestone, which it immediately underlies. In the 

 ravine at the northern extremity of the Dale, a somewhat analogous deposit is 

 found, surrounded by the lower coal-measures; and incumbent upon a very 

 compact basalt, divided into large irregular spheroids. A similar basalt appears 

 at nearly the same level, a short distance west of the Horsehays, near the centre 

 of the field. Proceeding northward, the coal-measures repose in places near 

 Ketley upon soft earthy trap and common and amygdaloidal trap. No outcrop is 

 visible ; but this superposition was discovered, some years since, in driving a 

 water-level from Ketley to the Old Park ; as it passed for the greater part of 

 the distance through an extremely hard crystalline basaltf . The level is aban- 

 doned, but it may be traced by the mounds of trap collected at the different air- 

 shafts. I could not learn that the coal-measures were altered by the proximity 

 of these igneous products ; and at the old pits at Little Wenlock, where the two 

 rocks are brought into abrupt juxtaposition by a large fault (No. 23 of Map), 

 intelligent colliers have assured me, that the coal shales and sandstone were 



* The soil formed by the disintegration of this deposit is extremely fertile. 



t Owing to the extreme hardness of this rock, Mr. Reynolds procured workmen from Der- 

 byshire, whence it is known as the Derbyshire level. As far as I could ascertain, the length of 

 this tunnel was about 1| miles, a great part of which passed through basalt and trap. 



