5l6 PHYSICAL GEOGRAPHY. 



Several features of this distribution are interesting. First, the rocks 

 have a general north-east south-west course. Second, they occupy the 

 spaces adjacent to and between the first areas of dry land, just as we 

 should naturally expect if the additions have been made to nuclei. A 

 more careful study of the arrangement shows that the same succession 

 of formations is observed in traversing either flank of the porphyritic 

 group. The same member touches both sides of the porphyritic area ; 

 the second lies adjacent to the first in each direction; the third is along- 

 side the second, connecting laterally, — and so on. Third, there are 

 several smaller areas of this age in the neighborhood. One occupies 

 Odell and vicinity. Another ranges through Essex county, Vt, and 

 probably exists as an underground ridge from Concord, Vt., to Reading, 

 Vt., where it seems to reappear and extend nearly to Massachusetts along 

 the same course. Small areas are situated about Bellows Falls and Pel- 

 ham. Another of great importance is the Green Mountain gneiss of 

 Vermont. The main range of New Hampshire stops short of the Ken- 

 nebec river, in a north-easterly direction, but seems to reappear on the 

 south-east in an extensive area between York and Hancock counties in 

 Maine. Fourth, this formation occupied several areas at the close of the 

 Atlantic age, which were concealed by the deposits of later eras. Such 

 are the Pemigewasset district at the White Mountains, and considerable 

 parts of Carroll, Strafford, and Merrimack counties. It is to be pre- 

 sumed, also, that the most distant areas, as the Green Mountains, and 

 coast of Maine districts, are connected directly with the New Hamp- 

 shire deposits by a sheet of sediments which bend down deeply into the 

 earth, directly overlying the porphyritic gneisses of the first period. 

 The space between the White and Green Mountains might then be 

 regarded as a great basin, or synclinal, held up by the porphyritic cup, 

 and itself sustaining various newer sheets of rock. Fifth, the general 

 height of the Atlantic rocks corresponds well with the average elevation 

 of the state above tide-water, except, — Sixth, the Mt Washington range 

 from the Saco valley to Mt. Bigelow in Maine. Its greater height is 

 probably due to additional elevations in later periods, while there is 

 reason to believe that it was raised to an unusual height at this time. 



Considered historically, the following notable events occurred during 

 the Atlantic period: i. There was a deposition of sediments between 



