446 



HISTORICAL GEOLOGY 



South America and Africa were similarly isolated at certain 

 times, but later in the Tertiary period they were linked with 

 the northern lands and thence received the tide of immigrants 

 belonging to the more advanced mammals. 



By studying the present distribution of animals and work- 

 ing out the paths of their earlier migrations, we can learn 

 much about the changes which have taken place in geography 

 during the later periods. The map (Fig. 456) shows roughly 

 how the continents and seas are thought to have been ar- 

 ranged in early Tertiary times, as compared with the present. 



QUESTIONS 



1. The Eocene coal in the vicinity of Seattle is bituminous and 

 locally even anthracitic ; that in Mississippi is soft lignite. With- 

 out further information, what predictions would you venture as to 

 the geological conditions in the two regions ? 



2. It has been suggested that the climatic changes known to 

 have taken place in the Tertiary period may have been caused 

 partly by changes in the ocean currents. What would happen 

 to-day if Florida joined Cuba and the Bahama Islands, while at 

 the same time Central America were submerged deeply ? 



3. Can you suggest why the known deposits of Eocene age are 

 largely those which were made on the surface of the land ? 



4. The accompanying diagram (Fig. 

 462) represents a mountain range in the 

 West. Show how the depth of erosion 

 early in the Tertiary may be estimated 

 from such a section. 



5. The Eocene strata of Wyoming 

 include beds of limestone with fossil 

 fishes. From your knowledge of Tertiary 

 geography what do you suspect was the 

 origin of these beds ? 



6. What events or conditions are recorded in the following sec- 

 tions (Figs. 463, 464, and 465) selected from the Tertiary strata in 

 different parts of the United States? 



7. The pyramids of Egypt were built 

 of Eocene limestone. What change must 



have taken place in this deposit of shells j? IG 453 Limestone 



since it was formed ? (Florida). 



FIG. 462. Section of moun- 

 tain range. The folded 

 beds are Paleozoic and 

 Mesozoic. The horizontal 

 bed is Miocene. (Vertical 

 scale, 1 in. = 10,000 ft.) 



