5l8 PHYSICAL GEOGRAPHY. 



This grand event closed the Atlantic period. Its importance demands 

 some further notice of the action of the forces producing elevation, and 

 the process of metamorphism. 



The Elevating Forces. 



Many persons think a mountain is elevated by some force or agent 

 situated directly underneath, and that the thrust is upwards, and the 

 mass of matter retained in place by an injection of molten matter. It is 

 difficult to comprehend how any such action can have taken place on a 

 large scale ; and hence we must avail ourselves of quite a different theory. 

 Its general application can be perfectly understood by reference to an 

 action common in the winter throughout the Northern states. 



When snow covers the ground, it is easy to push it away from a given 

 area; but a ridge is built up just on the edge of the cleared walk. Sup- 

 pose our assistant takes a pole, fastens it into the centre of a piece of 

 board, one foot high and three feet long. A single effort will enable him 

 to clear a space three feet wide by pushing the board away from him. 

 If three hundred men, each armed with a similar snow-pusher, should 

 act simultaneously along a sidewalk nine hundred feet long, there would 

 suddenly start into being a ridge of snow nine hundred feet in length. 

 The force of elevation in this case is a lateral one, and it accomplishes 

 the same result as if some power had acted upwards from beneath along 

 the same line. Now our theory supposes the existence of a mighty force 

 acting laterally along the whole length of the Atlantic formation, from 

 Canada to Alabama, in the same way that the ridge of snow was ele- 

 vated. The power displayed is great enough to shove along the thick, 

 horizontal sheet of sediments; and, where the substratum is firm, to 

 fold up a mountain range resting upon durable foundations. In case the 

 floor is yielding alongside of the range, a valley would be formed parallel 

 with the mountain. If the foundation is unyielding, there will still 

 naturally be depressions or valleys between the mountain ranges. 



The origin of this lateral force is suggested by certain geological 

 features of our vicinity, and general theoretical considerations, i. Given 

 the existence of the parallel older ridges of the Penobscot district in 

 Maine, the primeval archipelago in New Hampshire, and the Adiron- 

 dack hills in New York, and grant that some energy causes them to 



