36 GLACIAL GRAVELS OF MAINE. 



Briefly stated, the glacial gravels are found in the form of every kind 

 of ridge, terrace, cone, dome, heap, mound, and plain into which loose, 

 water-washed matter can be piled, and with both steep and -gentle slopes. 



Topographical relations. — Generally tliese deposits of water-assorted sand and 

 gravel are heaped up above the surrounding level. They also take the 

 form of flattish-top terraces on hillsides, or they may fill a valley from side 

 to side as a plain of IcA^el cross section but inclined longitudinally at the 

 same slope as the valley. They often form long systems Avith average 

 trend from north to south and nearly parallel with the glaciation. Some- 

 times they are found in the valleys of existing streams, but more often 

 where no ordinary surface stream larger than a mere brook can ever have 

 flowed, even in the time of the most violent floods. Many of the shorter 

 systems are only from 100 to 400 feet above the sea at their northern 

 extremities, while the longer systems originate at the north at elevations of 

 700 to 1,600 feet, a few ridges nearly 2,000 feet high being known. The 

 northern ends of the distinct systems are higher than the southern ends, 

 but the gravels do not follow a uniform slope. The map shows well how 

 often they leave the valley of a stream and pass over a divide or low col 

 into the valley of another stream. In so doing they not only rise above 

 the average grade line of the system, measured from one extremity to the 

 other, but they also rise in actual elevation above the sea. Throughout the 

 greater part of the State I do not know of any of the systems crossing 

 hills more than 200 feet higher than the valleys lying to the north of them. 

 But in the southwestern part of the State they repeatedh^ go up and over 

 hills 200 to 250 feet, in one case 400 feet, high (measured on the north). 

 Since the height of the hills which the gravel systems could surmount was 

 limited, they always penetrate higli ranges of hills by low passes. These 

 passes are not always the lowest that could have been chosen, nor are they 

 always the most direct. Probabl}^ in the larger number of cases the gla- 

 cial rivers took tlae best routes for getting from one end to the other, taking 

 both grade and dh-ectuess into account. 



An experienced engineer wishing to consti'uct a railroad between the 

 termini of the longer systems as economically as possible, by the shortest 

 route consistent with the minimum amount of rise and fall, would in a sur- 

 prising number of cases find himself following the same route as the gravel 

 systems. A good topographical or relief map of the State would reveal 



