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."[122] This statement is, with the exception of one locality, undoubtedly true.[123] 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. [Footnote 122: _Op. cit._ p. 131.] [Footnote 123: See note on next page.] Jukes further shows 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." 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 Palæozoic 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 younger formation, they should not be found penetrating it.[124] It seems almost certain that they must be of an age intermediate between the Coal-measures of South Staffordshire and the surrounding breccias and sandstones of the Permian series. And as there is clear evidence of contemporaneous volcanic action in the lowest part of the Permian system to the north in Scotland and to the south in Devonshire, the inference seems not unreasonable that these intrusive basalts of the Midlands are most probably of Permian age.