110 GLACIAL GRAVELS OF MAINE. 



and overlain by a delta-plain deposited by the glacial waters in an open 

 arm of the sea. 



• A series of high granite hills borders the valley of the west branch of 

 Union River on the east, and the osar, having crossed the Silsby Plains, 

 ends right in front of a very low and level pass between two of the hills. 

 For near a mile in this pass no glacial gravel could be found, but at the 

 east end of the pass the gravel begins again as an osar-plain one-eighth of 

 a mile or moi'e wide. The system is soon cut through by the middle 

 branch of Union River and then takes the osar form of a two-sided ridge 

 (PL V, A). This ridge rapidly enlarges toward the southeast and becomes 

 known as the Whalesback. It is one of the largest ridges of glacial gravel 

 in Maine, varying in height from 50 to 100 feet above the plain of marine 

 clay which deeply covers its base. For several miles a parallel smaller 

 ridge lies a short distance west of the main ridge, and the two are con- 

 nected by numerous cross ridges. Thus are inclosed numerous large kettle- 

 holes and swamps containing several acres. Among the local legends, I 

 find one to the effect that Agassiz was greatly interested in this huge ridge, 

 speaking of it to my informant as a moraine. The Air Line road from 

 Calais to Bangor is made on the top of this ridge for about 3 miles. The 

 ridge becomes lower toward the south, and the Whalesback is considered 

 to end at this low place, near where the Air Line road leaves it and turns 

 east.. The gravel does not end here, however, but continues on southeast- 

 ward along the valley of Leighton Brook, a tributary of the middle branch 

 of Union River flowing northwest, most of the Avay as a prominent 

 two-sided ridge. Tn the eastern part of T. 21 it escapes from the hilly 

 country into the great plain of the Narraguagus, which extends for many 

 miles to the sea. It at once expands into a series of low and broad reticu- 

 lated ridges, showing a gentle rolling and hummocky surface. Soon the 

 gravels become more level and horizontally stratified. They extend almost 

 continuously through Ts. 22, 16, and Deblois, into Columbia. Here and 

 there, rising above the horizontally stratified sediments, are ridges of 

 arched cross section that were evidently deposited within the ice walls. 

 Most of these plains from Rocky Pond and southeastward must be con- 

 sidered as a marine delta. From Columbia to Deblois, and perhaps still 

 farther northwest, the southern edge of the gravel plain ends in a steep 

 blutf and shows so many cobbles and bowlderets that it seems quite certain 



