14 SUMMER IN A BOG. 



sand and gravel will present its vast riches to 

 the needs of humanity. But how came they 

 here, and what is their story? 



Sometimes the digger into the rich black 

 muck of an alluvial tract has unearthed the 

 skeleton of a mastodon, an extinct species whose 

 remains are found also in far Northern lati- 

 tudes. 



Sometimes in the depths of the earth re- 

 mains of vast forests are brought to light and 

 give testimony. 



To the geologist the story is a fascinating 

 one, telling of a time when the climate of all 

 this Northern world was warm, tropical even. 

 Of a cataclysm, or, possibly, some orderly, 

 natural force, which reversed the conditions 

 and, during cycles of time which may be only 

 guessed, sent at intervals of cycles the slow 

 progress of ice sheets and glacial currents far 

 down — as far as the 38th parallel of latitude — 

 toward the tropics. 



Some winter night, when the mercury is 

 dropping to zero and below, when the flesh 

 shrinks and shivers in the unexpected blizzard, 

 let the fancy wander into the realms of possi- 

 bility and dream that another invasion of ice 

 has begun on earth. 



The natural gas and the coal laid in for 

 winter use have been exhausted, but the oold 



