istic plants, a study of the plant remains of any deposit will 

 give us an idea of its history. A study of the peat bogs of our 

 north Atlantic coast shows in several cases a layer of fresh 

 water peat beneath the salt water peat now forming on the 

 surface. This shows that the bays once stood above sea 

 level and were filled with fresh water. Subsidence set in 

 and the bays became salt. The fresh water plants were 

 replaced by salt water species and the present surface layer 

 of peat was started. 



The above features are all evidences of relatively recent 

 movements of the shore line. The clays, deltas and peat beds 

 are all unconsolidated and subject to rapid erosion when 

 elevated. Although only a short time has elapsed since the 

 retreat of the water, these deposits are already cut up and 

 partially removed by stream action. Even the sea cliffs and 

 terraces last comparatively only a little longer. Frost action 

 of the exposed rock will soon destroy the features of wave 

 erosion. For a study of the more ancient sea levels, those 

 which preceded the glacial period, we must turn to another 

 type of evidence. This is to be found in a study of the 

 summit levels of the inland hills and mountains. 



The striking feature of the landscape of the greater 

 part of New England is the almost level skyline. Although 

 the country is carved into hills and valleys, the hills rise to 

 practically the same level. Often they contain areas of 

 level land on their summits. This accordance of summit 

 level is independent of rock composition and structure. The 

 cause must be sought in some factor outside the rocks them- 

 selves. The explanation given was that the level hill tops 

 were the remains of a great plain which once covered most 

 of New England. Here and there isolated mountains rose 

 from this plain with one larger group, the higher peaks of 

 the White Mountains. This plain was formed by river 

 erosion. After this level surface was well developed it was 

 lifted and tilted. The revived rivers at once started to carve 

 the surface until it reached its present condition. During 

 this time, the Cenozoic Era, several plains were developed, 

 tilted and buried in the coastal region from New Jersey 

 south. 



In 1912 the late Professor Joseph Barrell read a paper be- 

 fore the Geological Society of America in which he pointed 

 out that the great plain of New England was not a single 

 plain, but a series of great steps with treads miles broad and 

 rises of a hundred or so feet. The hill tops are accordant 

 and form a level sky-line for several miles, then there is a 

 sudden increase in elevation of the hills with the tops ac- 



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