14 



THE AGE OF THE EARTH 



but sooner or later the familiar processes of denudation 

 and deposition started into activity, and have con- 

 tinued acting uninterruptedly ever since. The total 

 maximum thickness of the sedimentary deposits, so far as 

 I can discover, appears to amount to no less than fifty 

 miles, made up as follows : 



Feet. 



Recent and Pleistocene 4,000 



Pliocene 5,000 



Miocene 9,000 



Oligocene 12,000 



Eocene 12,000 



Cretaceous 14,000 



Jurassic 8,000 



Trias 13,000 



Permian 12,000 



Carboniferous 24,000 



Devonian 22,000 



Silurian 15,000 



Ordovician 17,000 



Cambrian 16,000 



Keweenawan* ... ... 50,000 



Penokee 14,000 



Huronian 18,000 



Man. 

 Pithecanthropus. 



Eutheria. 



Mammals. 

 Reptiles. 

 Amphibia. 

 Fish. 



Invertebrata. 



Geologists, impressed with the tardy pace at which 

 sediments appear to be accumulating at the present 

 day, could not contemplate this colossal pile of strata 

 without feeling that it spoke of an almost inconceivably 

 long lapse of time. They were led to compare its duration 

 with the distances which intervene between the heavenly 

 bodies ; but while some chose the distance of the nearest 

 fixed star as their unit, others were content to measure 

 the years in terms of miles from the sun. 



The stratified rocks were eloquent of time, and not to 



:;: It is very doubtful whether the Keweenawan possesses so great 

 a thickness as this. 



