A FEW WORDS ABOUT COAL. 303 



period onwards, even until our own, movements of the 

 earth's crust have been probably more irregular and 

 violent. But it would seem likely that, in the carboni- 

 ferous period, an intermediate state of things prevailed 

 when, owing to the greater heat of the earth's crust, 

 and consequently the greater relative thickness of the 

 plastic subterranean portions of the crust, the move- 

 ments were more steady, and affected wider regions 

 than at present, while the relief given by volcanic 

 craters, instead of being intermittent as at present, 

 was afforded uniformly and on a grander scale. 



If this were, indeed, the case, then, towards the 

 close of the carboniferous period, great disturbances of 

 the earth's crust might be expected to have taken place, 

 since that would be the time when the chief volcanic 

 vents ceased to relieve the pent-up subterranean forces. 

 This accords well with the condition of the geological 

 record. c The termination of the carboniferous forma- 

 tion,' says the author of the Vestiges of Creation, ' is 

 marked by symptoms of volcanic violence ' (by which 

 he evidently means simply subterranean violence), 

 c which some geologists have considered to denote the 

 close of one system of things and the beginning of 

 another. Coal-beds generally lie in basins, as if fol- 

 lowing the curve of the bottom of the seas ; but there 

 is no such basin which is not broken up into pieces, 

 some of which have been tossed up on edge, others 

 allowed to sink, causing the ends of strata to be, in 

 some instances, many yards, and, in a few, several 

 hundred feet, removed from the corresponding ends of 



