462 GLACIAL GEAVELS OF MAINE. 



into the ice to considerable distances. The region is crossed by two series 

 of valleys nearly at right angles. The principal streams flow eastward 

 along one series of valleys, and their lateral tributaries flow north or south 

 in the other series. The larger gravel series extend from north to south, 

 and thus are constantly going up and down hills, crossing the east-aud-west 

 valleys, or following up the north-and-south valleys to a divide and then 

 descending into another drainage basin. Man)?- of the cols they cross are 

 more than 200 feet higher than the land to the north. For 20 or 25 miles 

 the channels of these glacial rivers would for about half their length be 

 filled with slack water on the northern slopes and in the lower parts of the 

 valleys. 



As we trace the gravels southward we find them occasionally taking 

 the form of a broad two-sided ridge with arched cross section, but for most 

 of the distance they have either the form of the broad osar terrace or that of 

 the plexus of reticulated ridges. These different developments alternate with 

 each other in the course of the same gravel series, proving that they were 

 the work of a common river and are merely different types of sedimenta- 

 tion. Toward the south the hills become lower and the valleys broader. 

 Here the plains of reticulated ridges widen and become the prevailing type 

 of gravels ; yet here and there are small delta-plains in the midst of the 

 kame complex or at their flanks, while here and there the gravel forms 

 level plains — osar terraces. Often in this district the central ridge of the 

 plexus is very massive, rising 50 to 100 feet above the smaller ridges that 

 cover the plain at its flanks. The lateral slopes of the ridges are here 

 rather steep and the kettleholes so deep that in the forest they are very 

 dark and gloomy. Many of them are more than 100 feet deep. Still 

 going southward, we find on the average the ridges becoming broader, 

 lower, and more plain-like, while the kettleholes become shallow. Not 

 far above the contour of 230 feet the ridges become confluent, as an 

 undulating plain, which toward the south becomes more and more level 

 and the material becomes finer until it ends in a sand plain which in turn 

 passes into sedimentary clay. The belt of transition between the con- 

 spicuously reticulated ridges and the plains of marine clay varies from a 

 half mile up to 2 or 3 miles. In the narrower north-and-south valleys the 

 gravels more often take the form of the osar terrace than the plexus of 



