throughout the greater part of its extent by considerable 

 deposits of uncrystalline sediments. These are, however, 

 almost wholly of early Paleozoic age, and show that these 

 valleys are of very great antiquity. 



The rocks forming the subject of this paper occur wholly in 

 the more south-eastern of the two divisions, or sub-provinces, 

 above indicated. This division embraces that great deflection 

 of our Atlantic coast-line known as the Gulf of Maine. The 

 head of the Gulf of Maine is at Portland ; and its apparently 

 but slightly contracted mouth is guarded by the two salient 

 angles, Cape Sable and Cape Cod ; while the Provinces of 

 New Brunswick and Nova Scotia enclose its north-eastern end 

 as Eastern Massachusetts does its south-western. The line 

 joining the head of the Bay of Fundy and Plymouth, in 

 Massachusetts, may be regarded as the axis of the gulf, and is 

 about three hundred and seventy-five miles long, with a trend 

 approximating north-east and south-west. This line is of 

 fundamental importance in the structure of this region, a base 

 line for both geography and geology. The maximum breadth 

 of the gulf at Portland is one-third of its length, or one 

 hundred and twenty-five miles. The prevailing and all but 

 universal line of strike throughout this entire region, from 

 Rhode Island to the Gulf of St. Lawrence, as already stated, 

 is north-east and south-west, — parallel with the axis of the 

 Gulf of Maine. The rocks which meet the water of this large 

 gulf are, for the most part, ancient crystallines ; and, where- 

 ever these are exposed to observation, the indications are plain 

 that the gulf is the product of erosion, — has been carved from 

 the ancient strata by which it is bordered, — and is not the result 

 of a synclinal or other depression of this portion of the earth's 

 surface. The agent of erosion appears, at first sight, to have 

 always been the waves of the Atlantic, and to have acted 

 uniformly from the east toward the west. A study of the true 

 contours of this body of water, however, brings to light facts 

 which seem to militate against this view. An examination of 

 a Coast Survey chart of this region shows that the water does 



