AGE OF MAMMALS. 291 



quently many concentric moraines were formed. I have 

 spoken of the moraines as walls, but many of them are 

 broad and extensive, some of them being now the sites 

 of cities. The cities of Berne and Zurich stand on mo- 

 raines. Agassiz mentions a moraine through which a 

 river had made for itself a passage, and a village occu- 

 pies the moraine on both sides of the river. 



These ancient moraines, like those found at the pres- 

 ent time, are made up of boulders, pebbles, gravel, and 

 sand, indiscriminately mixed together. But their com- 

 position is concealed from view by the soil which has ac- 

 cumulated upon their surface in the many centuries, even 

 long ages, that have passed since their formation, and 

 the consequent vegetation that has sprung up upon it. 

 "Time," says Agassiz, "which mellows and softens all 

 the wrecks of the past, has clothed them with turf, grass- 

 ed them over, planted them with trees, sown his seed, 

 and gathered in his harvests upon them, until at last they 

 make a part of the undulating surface of the country." 



403. Soil made in the Post-tertiary Period. Soil is 

 merely comminuted rock. Nothing but the lowest or- 

 der of vegetation can grow on solid rock, and that in the 

 scantiest manner. The rock must'be broken and ground 

 up into soil in order to be the basis of a full vegetation. 

 The various agencies by which this is done have been 

 brought to your view in various parts of this book. They 

 have been at work at all times since the first rocks of the 

 Azoic age were formed, but at some periods more than 

 at others. They were especially at work in the Post-ter- 

 tiary period. Quite a large portion of the soil now cul- 

 tivated was produced then, and we may say that it was 

 one of the great objects of the Creator, in the operations 

 of that period, to provide soil for the gardens and fields 

 of man, who was to come upon the scene of action in the 

 following age. The rocks were broken and ground up 

 for this purpose by the glaciers and icebergs of the Gla- 

 cial period, and the work of grinding and sorting was 



