Page:The South Staffordshire Coalfield - Joseph Beete Jukes - 1859.djvu/150

132, however, this occurrence of igneous rock in them becomes no exception to the general statement given above.

The second argument is of a more positive character, and is this, that at whatever period these igneous rocks were produced, they were all existent before the production of the faults and dislocations that have traversed the Coal-measures, and before any great denudation had been effected on the country.

The northern end of the Rowley Hill basalt is distinctly cut off by the extension of the northern of the pair of Dudley Port Trough faults and the southern of those faults seem also to have affected it.

The sheets of greenstone that spread from below the Rowley Hills, through the centre of the district, up to Wednesfield and Bentley, always run pretty nearly in the same beds, at whatever depth those beds may be found, and however they may be broken by faults. This shows that the "green rock" is itself cut through by the faults and thrown up or down by them, as the case may be, exactly as the Coal-measures are affected by them.

The same may be said in general of the sheets of "green rock" proceeding at a higher level from Barrow Hill. In each case the "green rock" crops out to the surface, along with the beds in which it lies; although as its thickness is very irregular, and as it shifts its place now and then in the beds, cutting up or down within certain narrow limits, above or below a particular set of beds, that outcrop has a corresponding irregularity and want of continuity.

This proves the igneous rocks to have been equally and similarly affected with the Coal-measures by the two great actions of "dislocation" and "denudation."

It seems quite impossible to suppose that if the faults existed before the "green rock" was injected into the measures, that it would not have taken advantage of those fissures to have made its way to the surface along them, rather than have forced itself in among and lifted up and floated a thickness of several hundred feet of beds over an area of several square miles. But since it is known for a fact that it is itself dislocated by these faults, as shown in the Horizontal (Longitudinal) Sections (Sheets 23, 24, and 25), that fact is conclusive in favour of the rock having been cooled and consolidated before those faults were formed.

My friend, Mr. S. H. Blackwell, indeed, informs me, that in the district west of Russell's Hall, south of Lower Gornal, where there are a number of step faults close together, the green rock there was found to go up into those faults. It certainly did not go up very far along them, since I believe it did not injure or intrude into the Thick coal, which there lies at no great distance above the "green rock." It may have sent veins up into the superincumbent measures along certain lines of slight resistance, which afterwards were converted into faults; or it 1s possible perhaps, that small dislocations were then caused before the time when the larger and more general dislocation of the coal-field was