il 



RELATIVE LENGTHS OF EPOCHS 



AS KKPRESENTED BV THICKNESS OF ROCKS 



TERTIARY. l.iiOOft. 



CRETACEOUS. '2.500 ft. 



JURASSIC. 5,000 ft. 



TRIASSIC. 3.000 It. 



PERMIAN. 1,. -,110 11. 



CARBONIFEROUS. 



I-J.dOO ft. 



DEVONIAN. 4,000 ft. 



SILURIAN. 



7,1100 ft. 



ORDOVICIAN. 



15,000 ft. 



CAMBRIAN. 



ii;,ooo. 



PRECAMBRIAN. 



EMi'iil unkiiuwii. 



