Geology of Coalhrook Dale. 451 



worked up to their point of contact with the " black rock" or basalt^ without 

 presenting- the slightest alteration* ; neither is the regularity of the plane 

 of dislocation at all disturbed in this part of its course. (See Section 7,) 

 I am, therefore, inclined to consider that the basalt and trap were ejected 

 previously to deposition of the carboniferous series; and from the irregularity 

 of its surface and the thinness of the carboniferous limestone, that the latter 

 formation merely decreased the first inequalities, and that the coal-measures 

 of this portion of the field were deposited on an irregular bed, consisting either 

 of limestone or of igneous rocks. We have, however, elsewhere evidence that 

 the coal-measures have been affected by other igneous rocks of more recent 

 date. Thus along the boundary fault, although no trap crops out, it has been 

 met with at various points below the surface. I have been informed, that in 

 the boundary fault near Donnington furnaces and near New Hadley, a rock 

 similar to the nucleus of the Wrekin was found in making a shaft ; and at both 

 these localities the coal near this fault is altered into a sooty substance. At the 

 Madeley fault, near the Hay, the coal was in the same state, and the ironstone 

 was red as if calcined. In these instances the deteriorated quality of the 

 coal and ironstone, and the difficulty of excavating the hardened rocks pre- 

 vented the workmen from proceeding in a direction which might have ex- 

 posed more fully the cause of these changes. (See Sections 3, 4, 9.) 



Other small bosses of greenstone and basalt appear on the side of the canal 

 near the Horsehays, at Coalmoor Farm, Harris Coppice (Sec. 7, 8.), Saplin 

 Farm, &c. ; the two first protruding into the coal-measures, the last into the 

 Wenlock shale ; and that at Harris Coppice separating the two formations. At 

 the apex of the coal-field is the mass of igneous rocks forming Lilleshall Hill, 

 the last visible effort, in this district, of those disturbing agents to which we 

 probably owe the outcrop of the field. This hill consists of a nucleus of light 

 greenish claystone, passing into a reddish gray hornstone, surrounded by a zone 

 of greenstone porphyry, and therefore resembles in composition the Wrekin. 



The igneous rocks are not, however, confined to the angular area of the 

 carboniferous and Silurian series, for they protrude also through the new red 

 sandstone which surrounds it. At Kinley Wich, a boss of hornstone similar to 

 that forming the nucleus of the Wrekin projects through the sandstone. 



The most important outcrop of igneous rocks in the new red sandstone 

 occurs at Wrockadine, Seaton, Burcot, Rushton, and in Southward. It forms 

 a slightly hilly district, rising to the height of about 350 feet above the level 



* I had not an opportunity of inspecting this phenomenon underground, as the works have been 

 abandoned for some years. 



VOL. V. SECOND SERIES. 3 N 



