42 



area in the map (Fig. 20) and it will be noticed that all of New 

 York is within that area excepting the extreme sontlnvestern part 

 near the sontliern end of Chautauqua lake. 



Kot only is the soil peculiar within this district but there are many 

 small hills of clay or sand, or sometimes of both together (Figs. 26 

 and 27). They rise in hammocky form and often have deep pits or 

 kettle-shaped basins between, sometimes, when the soil is clayey 

 enough to hold w^ater, containing tiny pools. These hills extend in 

 somewhat irregular ranges stretching across country from the east 

 toward the west. The position of some of these ranges is indicated 

 on the map (Fig. 20). 



For a long time people wondered how this soil with its foreign 

 pebbles and boulders, all together called " drift," came to be placed 

 where they are ; they were especially puzzled to tell how the lai-ge 

 boulders, called erratics (Fig. 14), should have been carried from 

 one place to another. It was suggested that they came from tlie 

 bursting of planets, from comets, from the explosion of mountains, 

 from floods, and in other ways equally unlikely ; but Louis Agassiz, 

 studying the glaciers of the Alps and the country round about, was 

 impressed by the resemblance between the "drift" and the materials 

 carried by living glaciers. 



Agassiz, therefore, proposed the hypothesis that glaciers had car- 

 ried the drift and left it where w^e now find it ; but for many years 

 his glacial hypothesis met with a great deal of opposition because it 

 seemed impossible that the climate could have changed so greatly 

 as to cover what is now a temperate land with a great sheet of ice. 

 Indeed, even now, although all who have especially studied the sub- 

 ject are convinced, many people, even those who are educated in 

 some directions, have not accepted Agassiz's explanation, just as 

 years ago, long after it was proved that the eartli rotated each day, 

 many people still believed that it was the sun, not the earth, that 

 was moving. 



The glacial explanation is as certain as that the earth rotates. 

 For some reason, which we do not know, the climate chanojed and 

 allowed ice to cover temperate lands, as before that, the clima'-e had 

 changed so as to allow plants like those now growing as far south as. 



434 



