QUATERNARY 663 



where they occur, affording for the city dwellers many attractive 

 places for rest and recreation. (3) The bays of New England 

 have for the most part been modified by glaciation. (4) Karnes, 

 eskers, and delta deposits furnish gravel for roads and for concrete 

 where rocks suitable for these purposes were absent in preglacial 

 times. (5) Deposits of clay suitable for the manufacture of brick 

 are abundant in old glacial lakes and valleys. (6) Soils are some- 

 times more fertile and sometimes more sterile as a result of glaciation, 

 but the balance is in favor of the former. The mixing of soils from 

 different regions by glaciers is often beneficial, especially when 

 they contain fine fragments of fresh rock which, upon weathering, 

 furnish a constant supply of plant food. On the other hand, large 

 areas overspread by glacial sand and gravel are comparatively 

 worthless, and hilly regions are often covered with bowlders. Regions 

 such as central Kentucky and the valley of Virginia, for example, 

 would probably be injured were an ice sheet to pass over them, while 

 others, such as the Piedmont of Virginia, might be benefited. 



REFERENCES FOR THE EFFECTS OF GLACIATION 



Chamberlin and Salisbury, — Geology, Vol. 3, pp. 358-412. 



Von Engeln, O. D., — Effects of Continental Glaciation on Agriculture: Bull. Am. 

 Geog. Soc, Vol. 46, 1914, pp. 241-264; 336-355. 



Life of the Pleistocene 



As the dinosaurs culminated in the Jurassic and Cretaceous, so 

 the mammals attained their greatest size and variety in the Pliocene 

 and Pleistocene. " The early and mid-Pleistocene life of North 

 America is the grandest and most varied assemblage of the entire 

 Cenozoic Period on our continent. It lacks the rhinoceroses of 

 Europe, but possesses the mastodons, in addition to an array of ele- 

 phants more varied and quite as majestic as those of the Old World. 

 Great herds of large llamas and camels are interspersed with enor- 

 mous troops of horses. Tapirs roam through the forests. True 

 cattle (Bos) are not present, but imposing and varied species of bison 

 are widely distributed. An element entirely lacking in Europe is 

 that of the varied types of giant sloths, which were scattered all over 

 the country, as well as the great armored glyptodonts in the south. 

 Preying upon these animals are not only saber-toothed cats, but true 

 cats, rivaling the modern lion and tiger in size.' , (Osborn.) 



Our record of the life of the Tertiary and previous periods has 



