

CHAP. VI.] CARBONIFEROUS PERIOD. 97 



Again, although the area of deposition was constantly 

 widened by subsidence, yet the detritus brought down from 

 the higher to the lower levels was always sufficient to 

 counterbalance this depression. Further, it would appear 

 that all this material must have been obtained from the 

 surface of the land, and transported by fluviatile agencies, 

 for there could have been very little coast-erosion round 

 the borders of this land-locked sea. 1 Rain and frost must 

 therefore have been constantly at work on the surface of 

 these continents, disintegrating and dislodging the rocks of 

 which they were composed, while the rivers would be 

 chiefly employed in carrying off the detritus so prepared, 

 for the continued depression would have diminished their 

 erosive capacity by lowering the slope of their channels. 



It is a geological axiom that deposition is a measure of 

 detrition, and we may see, therefore, in this enormous mass 

 of sediments a measure of the detrition which took place, 

 and of the amount of material removed from those portions 

 of the great Carboniferous continent which drained into 

 that sea whose limits have been indicated above. 



Now the time necessary for the progress and consumma- 

 tion of all these natural operations must have been enor- 

 mous, and yet the geographical changes must have been so 

 slight and so slowly accomplished throughout this great 

 length of time that they did not materially alter the rela- 

 tive positions of land and sea, or interrupt the process of 

 swamp formation ; this, then, is the peculiar and remark- 

 able point in Carboniferous history which I desire to im- 

 press upon the reader's mind, that it was a period of in- 

 ternal quiescence, a period in which terrestrial disturbances 

 were at a minimum, and consequently when the surface 

 agencies of change were able to continue their course of 

 action to a greater extent than usual. Now their course of 



1 It is very probable that, as in the modern Mediterranean, the rise 

 and fall of the tide in this sea was very small. 



