2 
Guide to the Fossil Remains of Man 
RELATIVE LENGTHS OF EPOCHS CHARACTERISTIC HIGHEST 
AS EEPEESENTED BY THICKNESS OP EOCKS. ANIMAL LIFE. 
MAN". 
TERTIARY. 
1,600 ft. 
CRETACEOUS. 
2,500 ft. 
JURASSIC. 
5,000 ft. 
TRIASSIC. 
3,000 ft. 
PERMIAN. 
1,500 ft. 
CARBONIFEROUS. 
12,000 ft. 
DEVONIAN. 4,000 ft. 
SILURIAN. 
7,000 ft. 
ORDOVICIAN. 
15,000 ft. 
CAMBRIAN. 
12,000 ft. 
Mammals with developing brain. 
Reptiles with insignificant brain, 
adapted for every sphere of life. 
Reptiles with insignificant brain, 
gradually changing to overcome 
necessity for life in marshes. 
Amphibians in marshes. 
Fishes. 
) Water-animals without backbone. 
PRECAMBRIAN. 
Extent unknown. 
Table of Geological Periods to show the relative shortness of the time during which the 
development of the brain in backboned animals has been of fundamental importance. 
