CHAP. XXXII 
ERUPTIVE ROCKS OF THE MIDLANDS 
i°S 
the dolerite had been a lava of that age, it ought to be found lying con- 
formably on the Coal-measures. But this it does not appear to do. Making 
every allowance for the way in which an advancing current of lava might 
plough up soft sediment on the bottom of the sea or of a lake, we can hardly 
thus account for the very uneven surface of Coal-measures on which the 
sheet of igneous rock rests. If the Rowley rock he looked upon as a lava 
which flowed out at the surface, it must, I think, he assigned to a time sub- 
sequent to that of the Coal-measures, when these strata had been upraised 
and had suffered some amount of denudation. I confess, however, that the 
petrographical characters of the rock, the alteration of the coals which have 
been worked underneath it, and the abundant veins of “ white rock ” which 
there traverse the seams, induce me to regard this rock as forming no 
exception to the general rule in the Midlands, but as having been intruded 
as a sill, now laid bare by denudation. Its fresher condition may arise 
from its thickness, or from some other circumstance which has not been 
ascertained. 
We have now to consider the probable geological date of the various 
intrusions of basic igneous material which can be traced over so wide an 
area in the centre of England. In discussing the subject, Jukes pointed out 
that in the surrounding district “ no igneous rocks of any kind are found in 
any formation newer than the Coal-measures.” 1 This statement is, with the 
exception of one locality, undoubtedly true . 2 But on any view there must 
have been a long interval of time between the formation of the highest strata 
of the South Staffordshire coal-field and that of the lowest Permian deposits 
of the district. It is quite conceivable, though at present incapable of proof, 
that the extravasation of eruptive material took place after the close of the 
Carboniferous period and during the earlier part of the Permian period. 
Jukes further shows that “at whatever period these igneous rocks were 
produced, they were all existent before the production of the faults and dis- 
locations that have traversed the Coal-measures, and before any great 
denudation had been effected on the country.” This argument may be 
readily granted. But, so far as we know, many, if not most, of the faults 
traverse also the surrounding Permian and Triassic rocks, so that igneous 
masses protruded during those periods would be affected by the same 
dislocations. 
When we consider the history of Palaeozoic time in this country, and 
especially the proof, obtainable everywhere else in Britain, that volcanic energy 
became quiescent during the accumulation of the Coal-measures, we may well 
demand better evidence than has hitherto been forthcoming that any portion of 
the dolerites of the Midlands is of Carboniferous age. It is important to 
notice that though the dolerite sills and veins are so abundant in the South 
Staffordshire coal-field, coming even in many places up to the present surface 
of the ground, no single case has been observed where they rise into the 
Permian rocks that overlie the Coal-measures unconformably. It is difficult 
to believe that, had these intrusions taken place after the deposition of the 
1 Op. cit. p. 131. 2 See note on next page. 
