232 On the Surface Geology of the Bas-in of the 



to the formation of great glacial masses of ice, i. e., a broad 

 evaporating surface of warm water swept by westerly winds 

 that carried all Buspended moisture immediately on to a moun- 

 tain belt, which served ns a sufficient condenser. 

 This, at least, may be positively asserted in regard to the 



icy of ice in the excavation of the lake basins, that their 



bottom.- and Bides, wherever exposed to observation, if com- 



I of resistant materials, bear indisputable evidence of 



ice action, proving that these basins were filled by moving 



glaciers in the last ice period if never before, and that part, al 



\ of the erosion by which they were formed is due to 

 these glaciers. 



No other agent than glacial ice, as it seems to me, is capable 



Kcavating broad, deep, boat-shaped basins, like those which 

 hold our lakes. 



If the elevation of temperature and retreat northward of the 

 glaciers of the lake basins were not uniform and continuous, 

 hut alternated with periods of repose, we should find these 

 periods marked by excavated basins, each of which would serve 

 to measure the reach of the glacier at the time of its formation, 

 the lowest basin being the oldest, the others formed in su< 

 sion afterwards. Such a cause would be sufficient to ace. unit 

 for any local expansions of the troughs of the old ice rivers. 



Where erlaciers flow down from highlands on to a plain or 

 into the sea, the excavating action of the ice mass musl termi- 

 nate somewhat abruptly in the formation of a basin-like cavity, 



ond which would be a rim of rock, with whatever of debris 



the glacier baa brought down to form a terminal moraine. 



When glaciers reach the Bea, the greal weight of the ice 

 mass musl plough np the Bea bottom out to the poinl where 

 the greater gravity of water lifts the ice from it.- bed, and bears 

 it away as an iceberg. 



[fit i- true, as the facts I have cited indicate, that our lakes 



are but portions of greal excavated channel- locally filled with 



rial, the fiords of the northern Atlantic and Pacific 



