DISCORDANCES EXPLAINED 299 



slow- wearing action of the rivers which now through 

 them, and the waves of the sea were shown to be capable 

 of cutting down cliffs and of reducing the land to a plain. 



From these facts the discordance in the succession of 

 stratified rocks found an easy solution. Recurring to the 

 instance of the Carboniferous rocks and their relations to 

 the Trias, we no longer need suppose that the stupendous 

 force which folded the Carboniferous rocks and raised them 

 into the air, acted suddenly or even very rapidly ; judging 

 from the rate at which mountains rise now, their upheaval 

 may have proceeded slowly ; a few feet in a century 

 would suffice. If we allow but one foot in a century, 

 it would only require two millions of years to produce a 

 mountain range 20,000 feet in height. The movement 

 might naturally be expected to be accompanied by earth- 

 quakes, possibly on a much grander scale than those 

 of the present. During its slow elevation, the mountain 

 range would be exposed to wind and weather, rain and 

 rivers would carve it out into ridges and valleys, and frost 

 would splinter its peaks into spires and pinnacles. Sub- 

 sequently it would sink beneath the sea, and the waves 

 of the sea, as they battered down its cliffs, would remove 

 the last remnants which had escaped the rain and rivers, 

 and roll over an unbroken plain. On this plain, as it 

 continued slowly to subside beneath the sea, the immense 

 deposits of the Trias, Lias, lower Oolites, and Oxford 

 clay would be piled up. 



If the rise of the sea-floor into the Bristol Alps took 

 place slowly, and involved a great lapse of time, so equally 

 did the sinking of the land to form the sea-floor afresh, 

 and in this long interval time was afforded for great 

 changes in the organic world ; and thus we reach an 

 explanation of the great and striking differences which 

 distinguish the fossils of the Carboniferous rocks from 

 those of later date. 



