The intrusive sheets, dykes, and veins of "green rock" and "white rock" trap which burrow in the lower measures about the Thick coal and beneath it on the northern side of the Rowley Fills, and seem to spread through the centre of the district as far north as Wednesfield and Bentley, and thereabouts, may have commenced their intrusions some time before the outpouring of the Rowley basalt, which, giving a sensible and large relief to the struggles of the volcanic matter below, may have terminated the igneous action.
There may also be seen, in the neighbourhood of Barrow Hill, rocks having the character of ash or trappean débris, and it ma be that that outburst of basalt likewise reached the surface, though from its position above the Thick coal it would appear in that case to have taken place at a rather earlier period than that of Rowley.
About Pouk Hill, there is no appearance of ash, and it seems to be so intimately associated with the horizontal sheet of greenstone, a short distance below, that I am more inclined to look upon that as a boss proceeding from it, not to the surface, but only towards the surface, and consolidating in an isolated mass at no great distance perhaps, below the surface of the rocks that existed at the period of its formation.
In all cases the isolated masses that are found in the higher parts of the Coal-measures are. I believe, basalt, while the wide spread horizontal sheets of igneous rock that spread over such large areas below, and occasionally make their appearance at the surface where the lower measures crop out, as about Wednesfield and to the east of Pouk Hill, are greenstone.
it is not by any means intended to insist too strongly on the superficial formation of the Rowley or Barrow Hill basalt, since except the occurrence of the ashy-looking beds, and the 'basalt being always above the greenstone, "there 3 is no conclusive evidence to show that these basaltic masses were not also intrusive sheets of igneous matter injected in between the beds of the Coal-measures.
If the basalts were outpoured lava streams, it of course follows that all the igneous rocks, taken az a whole, were contemporaneous with the Coal-measures, taken as a whole.
Even on the supposition of the igneous rocks being all intrusive, and therefore formed subsequently to the formation of the beds between which they now lie. I still think that we cannot assign a much later age to them, and that we shall be compelled to consider them as older than the Permian rocks.
The first argument in favour of this conclusion is a negative one, namely, that in this district no igneous rocks of any kind are found in any formation newer than the Coal-measures.
So long as the red clays of Essington Wood were considered to be of Permian age, this argument failed us as regards that formation, since there is a little boss of a peculiar kind of greenstone to be seen in a small quarry just west of the brickpits of that place. Now that these red clays are proved to be Coal--
