Unconformity. 35 



apart, while the Bristol and Somersetshire coal-field is 

 separated from both by the estuary of the Severn. 

 These separations have been brought about by the 

 agency of long-continued denudations, which have 

 swept away thousands of feet of strata bent into 

 anticlinal and synclinal curves in the manner shown 

 at x in fig. 7, p. 33, and fig. 115, p. 601. The coal-field 

 of the Forest of Dean has thus become an outlier of the 

 great South Wales coal-field ; and the Bristol or Somerset- 

 shire coal-field forms another outlier of a great area, of 

 which even the South Wales coal-field is a mere frag- 

 ment. Such denudations have been common over large 

 areas in Wales and the adjacent counties, and in many 

 another county besides. 



Observation and argument alike tell us that we need 

 have no hesitation in applying this reasoning to all 

 hilly regions, whether formed of stratified rocks alone 

 or intercalated with igneous rocks, and thus we come 

 to the conclusion that the greater portion of the rocky 

 masses of our island have been arranged and re-arranged 

 under slow processes of the denudation of old, and the 

 reconstruction of newer strata, extending over periods 

 that seem to our finite minds almost to stretch into 

 infinity. 



Unconformable stratification, when its significance 

 has been realised by the student, cannot fail at once to 

 impress on the mind a sense of the degradation of 

 strata in some old epoch similar to that which is now 

 going on, and I know of few objects that speak more 

 eloquently of geological time. 



In the following diagram No. 1 represents an old land 

 surface, in which perhaps beds of sandstone and slate 

 or shale have been upheaved at a high angle. Let us 

 then suppose that, by the wasting power of weather and 



D 2 



