ELEVATION AND SUBSIDENCE. 63 



(1) Wholly fictitious appearance of changes of level; (2) phenomena pro- 

 duced by local changes in tidal heights without any real change in the general 

 level of either land or sea; (3) phenomena really produced by a sinking of the 

 land, but so long ago that they can not properly be cited as proofs of subsi- 

 dence within the last few thousand years. The fictitious appearance of change 

 of level is given by (1) standing forests killed by the invasion of the sea; (2) 

 submerged stumps; (3) submerged peat. Lyall, Cook, Gesner, Ganong, and 

 others have regarded dead standing forests as conclusive evidence of the sub- 

 sidence of the Atlantic coast. Goldthwaite found that death resulted in some 

 cases from fire and in others from a local rise in the high-tide level. Johnson 

 ascribed three distinct causes for the death of the forests about Cascumpeque 

 Harbor in Prince Edward Island. Accumulations of sand in the forest caused 

 the ponding back of storm-waters, and the consequent death of the trees. 

 Elsewhere, small waves had eroded the earth from the tree-roots and exposed 

 them to salt water. Finally, the number and width of the inlets ki the barrier 

 beach had caused a local rise in the high-tide surface and a consequent inva- 

 sion of the forest by salt water. The author explains the presence of live 

 cypresses in water often over 5 feet deep by finding that the spreading bases 

 were just above water-level at the same elevation as on the adjacent low shore, 

 and that the submerged parts were really spreading roots. The trees had 

 grown on a low coast composed of peaty soil, and the erosion of the latter by 

 the waves had left the trees standing in water. 



Submerged stumps are found to arise in a variety of ways independently of 

 coastal subsidence. Along the shores of South Carolina and Georgia, smaQ 

 waves undermine the trees and let them down into salt water, often in the 

 erect position. The trunks later break off at the water-line and leave upright 

 submerged stumps. Similar stumps are also produced by the long tap-roots 

 of certain trees, such as the loblolly pine. Submerged stumps, due to a local 

 rise of the high-tide level, to the compression of peat-bogs caused by a lowering 

 of the ground-water level as the waves cut into the shoreward side of such 

 bogs, to the compression of deposits due to the weight of barrier beaches, as 

 well as to many other causes, have been observed. It is also pointed out that 

 beds of submerged peat containing stumps may be caused by the s inkin g of 

 floating bogs, by the lowering of the ground-water and the consequent lower- 

 ing of the surface of the bog when the latter is encroached upon by the sea, 

 or by the weight of a barrier beach, compressing the peat so that it is exposed 

 at or below tide-level on the seaward side of the beach. 



The phenomena produced by a local rise in the high-tide level are explained 

 in detail. A bay nearly separated from the sea by a barrier beach, but con- 

 nected with it by a narrow tidal inlet, will have a lower high-tide level. Trees 

 and other vegetation will grow down to the high-tide level of the bay, and hence 

 below the high-tide level of the sea. Whenever a large breach is made in the 

 barrier beach the high-tide level will become the same in the bay as for the 

 sea. All trees whose bases are below this high-tide level will be Idlled and will 

 later be represented by submerged stumps. The surface of the salt marsh will 

 build up to the new high-tide level, enveloping stumps and other plant remains. 

 Fresh-water peat may also be buried under a layer of salt-marsh peat. Change 

 of high-tide level with the killing of forests have actually been observed, as 

 near Boston in 1898, when a large opening was made in a barrier beach by a 

 storm. 



Appearances of subsidence predominate over those of elevation because 

 marsh deposits tend to sink to the new level when the high-tide level is 

 lowered because the immediate destruction of fresh-water vegetation by salt- 

 water when the high-tide limit is raised is more striking than the slow recovery 



