SIZES OF GLACIAL RIVERS. 293 



State He computed the annual discharge of the present rivers of Maine 

 at 1,229,200,000,000 cubic feet, or 3,368,000,000 cubic feet daily. This 

 represents a precipitation of about 3^ feet per annum. 



Obviously in glacial times that portion of Maine which was within the 

 area of accumulation or h^v^ had less water discharge than the precipita- 

 tion, the surplus being pushed forward as flowing ice into the zone of melt- 

 ing. The position of the ndv^ line would determine the ratio, at any given 

 time, of water discharge to the total precipitation over the area now under 

 consideration. The location of the nivi line during the time of thickest ice 

 is uncertain. The glaciation of the islands off the coast proves that at one 

 time the ice advanced out into the Giilf of Maine. Later, at a time when 

 the ice had retreated before the rising sea nearly or quite to its coast, great 

 glacial rivers were pouring into the sea and were depositing in open tide 

 water the largest marine deltas in the State. Here and there we find marine 

 deltas south of this line, proving that the glacial rivers had previously to 

 this time been pouring into the sea at various points in the course of the 

 retreat of the ice. At the time the ice front had receded as far north as 

 the present coast line the whole coast region of Maine to a breadth of 100 

 miles must have been in the zone of wastage, and either at this time or 

 later the whole State was in this zone. 



The melting of the great body of ice that covered the land and was 

 continually renewed by flow from the north would of itself give a large 

 melting-water discharge over the zone of wastage. To this must be added 

 the precipitation over the zone itself During part, perhaps all, of the 

 period after the ice had retreated to the present coast line, the land stood at 

 less elevation in Maine than at present. This would tend to lessen the pre- 

 cipitation, but only in small degree. On the other hand, during a part, at 

 least, of this period the sea advanced so far up the St. Lawrence and Cham- 

 plain valleys that ISlew England was a peninsula or island unusually 

 accessible to moisture from the ocean. 



Whether we look, then, at the great quantity of the glacial gravels, or 

 at the large size of the stones and bowlders transported, or at the broad 

 plains of valley drift which were often deposited while ice still lingered to 

 the northward, or at the local geographical conditions, or at the climate 

 prevailing at or about this time in various parts of the country, we find that 

 everywhere the field phenomena require a large supply of water. The 



