524 Geological Society: Anniversary Address, 1843. 
Igneous Rocks of South Staffordshire—As connected with the 
older depositary rocks of the central counties of England, I will now 
direct your attention to some recent observations on the changes to 
which they have been subjected by igneous agency. Besides form- 
ing a most instructive museum, singularly rich in Silurian and Car- 
boniferous species (including many unpublished), the Geological 
Society of Dudley, to the establishment of which I last year alluded, 
has produced a report ‘On the Igneous Rocks of the South Staf- 
fordshire Coal-field*,’ not yet printed, with the results of which I 
am convinced you will thank me for making you acquainted. In 
the southern portion of this coal-field there are centres of eruption 
where the basaltic and trappean matter, rising from the bowels of 
the earth, completely cuts through the surrounding carboniferous 
strata, dislocating and altering them in the manner which has been 
pointed out by Mr. Keir, Mr. Arthur Aikin, and other observers, 
including myself. In regard to the lateral injections of the igneous 
matter among the coal strata, Mr. Blackwell, by comparing the 
shaft-sections of contiguous collieries, has shown, that however a 
single vertical section might seem to afford grounds for belief, that 
such igneous matter had been formed as a bed, yet that in reality it 
traverses various depositary strata in a slightly oblique direction, 
and often thins out in the form of awedge. From such apparently 
horizontal masses, vertical dykes, with occasional lateral veins of 
white felspathic rock, varying in thickness from a few inches to 
three or four yards, are seen to rise up and traverse the coal-beds 
in the most irregular manner, though such dykes are not found to 
produce any derangement in the regular measures. Another good 
fact observed in relation to a supposed horizontal sheet of basalt in 
the midst of the sedimentary strata, is, that the beds on which it 
rests are less subject to faults and dislocations than those which lie 
above it; the intruded mass, indeed, sometimes rising up to the 
surface and forming a knoll, occasionally bare, and at other places 
covered by the coal strata, which mantle round it. 
The report also proves, that some of the chief faults which radiate 
from one of the great centres of eruption (Barrow Hill), were produced 
contemporaneously with its elevation ; since the basaltic matter which 
flows laterally in apparent beds, follows the line of fault, bending and 
leaping up, as it were, without a break from lower to higher levels. 
From this fact Mr. Blackwell infers, that the basaltic matter must 
have been in fusion when it was extruded laterally along the sur- 
faces of certain strata, but that the subsequent dislocation by which 
these beds were moved to different levels, took place before the 
igneous matter had cooled and when it was still plastic. This very 
remarkable phenomenon, which is indeed similar to examples cited 
by Dr. Mac Culloch, is an exception to the cases in other parts of the 
district (Wolverhampton), where the beds of basalt are broken off and 
change their relative places with the coal strata; and thus we learn 
* The Report to which allusion is here made, including the Sections, was 
drawn up by Mr. J. H. Blackwell of Dudley, assisted by Mr. W. Spencer, 
