SUMMARY OF THE SALOPIAN COAL-FIELDS. 



139 



or volcanic origin, since every part of their surface exposes nothing but fragments of 

 the same substances ; and as none of these fragments have the slightest appearance of 

 having been transported, but preserve the utmost sharpness and angularity of form, 

 there is no doubt that they have resulted from the rock having a natural tendency to 

 break into such forms. Occasionally, indeed, the fragments have been re-cemented 

 into a sort of coarse superficial breccia (exclusively trappean) , of which a good example 

 is to be seen in one of the narrow ravines on the eastern and wooded flank of Stagbury 

 Hill. The coal-measure strata in the vicinity of these hills being highly dislocated, it 

 would appear that the trap of which they are composed must have been erupted after 

 the consolidation of the carboniferous deposits. Again, as fragments of the same trap 

 often form a part of the central members of the New Red Sandstone, it is clear that the 

 eruption in question must have taken place as alluded to in the sixth chapter, either 

 towards the close of the one epoch, or in the commencement of the other ; and thus 

 we obtain geological limits for the date of these eruptions. 



Having described the various intrusive rocks of this tract, let us consider for a mo- 

 ment the general relations of the deposits of the Forest of Wyre, and then take a short 

 review of the principal phenomena in the Salopian coal-fields of this vicinity. 



The strata of the Forest of Wyre cannot be considered as forming different basins, 

 but simply as carbonaceous masses which were originally deposited upon an unequal 

 surface of Old Red Sandstone, without the interposition of the carboniferous limestone. 

 Since that period, the strata having been penetrated at many points by rocks of volcanic 

 origin, the whole country underwent numberless convulsions, by which the former 

 relations of these deposits have been much modified, and their beds thrown into un- 

 connected patches. From what has already been stated, the reader may doubtless 

 have inferred, that this and the other Salopian coal-fields are well exposed only in the 

 contiguity of certain eruptive rocks, and that as they dip in many places beneath the 

 Lower New Red Sandstone, vast carbonaceous deposits may now lie concealed by that 

 formation in positions where they have not been thrown up by volcanic action. Other 

 decisive proofs of this arrangement of the strata, so important to the future develop- 

 ment of our national mineral resources, will be brought forward in the chapter on the 

 great Staffordshire coal-field. 



Independent, however, of the phenomena resulting from igneous action and dis- 

 turbance, the following data have been established in respect to these Salopian coal- 

 fields : — 



1st. The proof of a younger zone of coal passing upwards, and conformably into 

 the lower members of the New Red Sandstone, and containing within it a peculiar 

 freshwater limestone, always occupying in a long course the same position. 



2ndly. The Coal Brook Dale field has been shown to contain, not only this upper 

 carbonaceous zone, but further a full development of the older coal strata, charged with 

 a mixture of freshwater, terrestrial, and marine remains, indicating an estuary origin. 



