THE PEAT CLISTASE. 



403 



swamps, in some are found species of the upland, while others indicate an open 

 marsh-like vegetation with sparse oak, birch, and pine. 



Davis (1910) has studied the salt marshes near Boston, and concludes from 

 the plant remains in the peat that many of them show unmistakable evidence 

 of fresh-water origin: 



The peat contains much woody material, including large pine stumps. 

 Where the peat contains salt-marsh material, the species were those that grow 

 to-day at or near high tide, and not eel-grass and other forms which grow 

 submerged or at half-tide. The existing marsh flora consists of two zones : a 

 salt-thatch zone consisting of Spartina glabra alterniflora and covering tidal 

 banks down to about half-tide mark. The next zone forms the general surface 

 of the marsh and is submerged an inch or two for a few hoxu-s every day. It 

 consists for the most part of Spartina patens and Distichlis spicata. The 

 remains of the three dominant marsh-grasses are easily recognizable in the peat. 

 The author concludes that the sea-level has increased progressively, or the 

 land has subsided, and that the deposits show the amount of subsidence. 

 They show, moreover, the rate of subsidence, since if the sinking were faster 

 than the upbuilding of the turf, Spartina glabra or marine forms would replace 

 Spartina patens. If it were slower, plants of drier zones would replace Spar- 

 tina patens. The deepest peat deposit was found at Nahant, where 12 feet of 

 salt-marsh peat were found overlying 2 feet of fresh-water peat, indicating that 

 the land was at least 16 feet higher when the fresh marsh existed than it is at 

 the present time. 



TwenJiofel (1910) has studied the peat-beds of Anticosti Island with reference 

 to the question of the origin of coal by deposition after transportation, and 

 deposition by growth in place: 



The peat deposits of the island vary in thickness from 2 to more than 10 feet, 

 and cover practically its entire surface. In many areas the peat is very black, 

 well compressed, and of good quality, showing under the microscope few traces 

 of the constituent plants. The conditions that have permitted the develop- 

 ment of these extensive peat deposits without an imderlying soil are due to a 

 combination of factors none of which are uncommon. The island is mostly 

 covered with a dense coniferous scrub in which the individuals have very pre- 

 carious foothold, with the result that the wind blows them down except in 

 sheltered areas. Some areas are treeless and bear a tangled growth of low 

 shrubs or are covered with mosses and herbs. It is thought that too great an 

 emphasis can not be placed upon the fact that here in the relatively cold 

 climate pf Anticosti exists a heavy annual growth of vegetation which is 

 yearly added to the peat under conditions which practically prohibit oxidation. 

 As a consequence, it seems that a warm climate is not an essential condition 

 for the great accumulation of peat," a fact recognized by Darwin in Tierra del 

 Fuego and the Falkland Islands, and by Russell for Northern Alaska. A 

 second conclusion reached is that deposits of coal of continental origin may 

 have many of the characters of marine deposits, and that, in interpreting the 

 origin of a coal-bed, the presence of marine fossils and great uprooting of 

 trees are not necessarily conclusive evidence of marine origin, nor even deter- 

 mining evidence against continental origin by growth in situ. 



