14 North American Forests and Forestry 



temperature, humidity, and so forth. The other fac- 

 tor is historical, arising out of the order in which the 

 seeds of different species were deposited in each 

 particular locality, or failed to be so deposited. 



The palaeobotanists, drawing their conclusions 

 from the remnants of wood, impressions of leaves, 

 flowers, and fruit, and other small relics of extinct 

 vegetation which are found imbedded in rocks and 

 beds of coal or peat, have established the fact that 

 during what are known as tertiary times, vast for- 

 ests, composed of trees not very different from 

 those now growing in the United States, existed in 

 far northern regions, nearly up to the pole, where 

 now everything is decked with ice and snow. But 

 the warm climate of the tertiary ages was succeeded 

 by the secular winter, which is known as the glacial 

 period of the quaternary epoch, and of which most 

 of my readers have heard. Farther and farther 

 south crept the great glaciers, joined by those flow- 

 ing down from the high mountains of the west, 

 until the whole northern part of the continent, as 

 far south as the latitude of Cincinnati, and even 

 beyond, was covered with a sheet of ice of immense 

 thickness, leaving but here and there an island un- 

 covered, like the celebrated driftless area of South- 

 western Wisconsin. Before the advance of the ice 

 and the cooling of the climate that was both cause 

 and consequence of the glaciation, the forests suc- 

 cumbed, and the species composing them were either 

 extinguished or became restricted to more southern 

 latitudes. But after thousands of years the climate 



