482 GLACIAL GKAVBLS OF MAINE. 



to Monctoa, New Brunswick, whence it turns backward, running nortliwesterly and 

 northerly, crossing the St. Lawrence estuary about halfway between Cape Gaspe 

 and the Saguenay. 



The 600-foot isobase is probably to be drawn from Georgian Bay iJast the outlet 

 of Lake Ontario, through the southern part of the Adirondacks, and thence east- 

 northeast nearly to Moosehead Lake. Here it makes an abrupt bend to the north 

 and west, similar with the loop of the 300-foot isobase at Moncton, and runs first 

 westward to some point not far from Three Rivers, and thence, turning again north- 

 eastward, it passes along the north shore of the St. Lawrence estuary.' 



Manifestly this metliocl is not complete until the elevations of all the 

 traceable beaches are accuratelj determined, and thereby the amount of 

 local warping, if any. 



The position of the shore line in any of the inland valleys would, 

 according to this method, lie where the profile of the valley, drawn in a 

 plane perpendicular to the lines of equal elevation, intersects the hori- 



, ^ zontal line marking the old 

 ' "~'- — ^ ; -^ sea level. Thus in the dia- 



FiG. 36.— Diagram illustrating tbe method of flutliugtlicliigliest sea level in gram tllO line 0C& repre- 

 sents the profile of a valley 

 supposed to be normal to the lines of equal elevation. At & and c are 

 raised beaches, and the profile is at these points depressed below the hori- 

 zontal line distances proportional to the heights of the beaches at those points. 

 This determines the position of the point a, which marks the former shore. 

 4. The elevation of marine deltas. The deltas of the interior at 300 

 to 350 feet are now interpreted Ijy me as marine, but possibly this point 

 may be disputed. They certainly do not bear such relations to the fossil- 

 iferous clays as the deltas nearer the coast. But sheets of clay and sand 

 are found extending from the deltas up to considerably higher elevations, and 

 therefore under no conditions do the deltas mai'k the highest level of the 

 sea. Indeed, it should be expected that deltas would be formed in front of 

 the ice, often at a considerable depth beneath sea level. The higher deltas 

 are more than 100 feet above the highest fossil thus far found. Marine fos- 

 sils are found in Lewiston, Winthrop, Norridgewock, Skowhegan, Palmyra, 

 Unity, and other interior towns. The highest deltas are found only a few 

 miles beyond the fossils. Both together constitute valuable collateral evi- 

 dence of the presence of the sea in the interior valleys, but do not give 

 the extreme limit. 



'Am. Geol., vol. 9, p. 248, April, 1892. 



