A CONTRIBUTION TO THE GEOLOGY OF SOUTHERN MAINE 525 



artificial. It was thought that possibly there might have been 

 a reversal of drainage brought about by glacial agencies, the 

 Back River and Adams Pond valley having formerly drained 

 southward. This seems clearly not to have been the case. 

 There is more or less sand about the southern end and sides of 

 Adams Pond, but nothing resembling a moraine and nothing in 

 the way of drift that could possibly have blocked a stream. 

 The valley widens northward and has every appearance of being 

 a normal ' erosion valley developed with the drainage in its 

 present direction. That it is pre- Glacial is evidenced by the 

 presence of both material and striae. The east-and-west Oven 

 Mouth on the other hand is a very narrow cut with precipitous 

 sides. Three tributaries enter it, two from the south and one 

 from the north, and the tributaries have a much older topo- 

 graphic expression than the Oven Mouth itself. This is clearly 

 due to the fact that the tributaries are developed along the 

 strike and have advantageous courses, while the Oven Mouth is 

 on a joint and cuts across hard layers. There seems no reason 

 to doubt that these tributaries originated after the Oven Mouth, 

 the latter being for practical physiographic purposes, the ocean, 

 and the streams developing as similar streams might arise on an 

 island. But the relation of the larger Back River valley to the 

 Oven Mouth is not so clear. It might have been developed like 

 the tributaries as a normal river valley subsequently drowned, 

 but since the Back River is pre-Glacial, on this supposition the 

 Oven Mouth would of necessity be pre-Glacial too, and the latter 

 is a very steep-sided gorge. It would seem that this and the 

 many similar streams in Maine must date their origin from a 

 time when the slope of the land was somewhat different from 

 what it is at present. The entire surface must actually have 

 been higher than at present, but with relative depression towards 

 the north. The recent drowning has led to the connection of 

 these various valleys by way of much younger tributaries along 

 the joints. 



Sea cliffs are notable features of the present erosion cycle. 

 These present interesting variations with respect to the kind 

 of rock involved and the direction of the structure. The granite 

 and the schist each has its particular topographic expression, 



