26 NEW YORK STATE MUSEUISI 



New York, though the " vleys," or swampy borders of the Hudson 

 come under that head. 



Upland swamps. Upland swamps are found in regions which 

 are approximately level. In a region where the surface does not 

 have a fall of more than 4 or 5 feet to the mile, any vegetation 

 which may spring up has a tendency to retard the flow of the rain- 

 water. When leaves or the trunks of trees fall, they act as a 

 sponge and retain the water, thus furnishing better conditions 

 for the growth of mosses and grasses. If the plain is originally 

 a woodland, the forest may be destroyed by the swampy condi- 

 tions thus produced, or it may be replaced by a growth of the 

 trees that are ordinarily found in swamps. It may seem far- 

 fetched to call such a swamp a modification of a lake swamp ; but, 

 when one consideTs that every fallen twig and every root is a dam 

 which holds back the water, it is apparent that the whole area 

 is made up of little lakes which furnish the proper conditions 

 for the growth of the swamp vegetation. In such a swamp the 

 rush and cat-tails stage may be entirely lacking, and the sphagnum 

 and grasses will be the most important factors in the swamp 

 formation. 



Climbing bogs. Climbing bogs are the natural spread of any 

 swamp to higher levels on account of the great amount of moisture 

 that is absorbed by the sphagnum and other mosses of the swamp, 

 but they are of no importance in this State. 



Ablation swamps. Ablation swamps, otherwise known as corro- 

 sion spring swamps, are not common, but are caused by the gradual 

 subsidence of the surface of the ground on account of the solvent 

 action of water on either the surface rock or some of the under- 

 lying strata, forming a pool or depression in which swamp vege- 

 tation springs up. The solution of salt and gypsum in central 

 and western New York is without doubt an important factor in 

 the formation of swamps in that part of the State, though in most 

 cases other causes have an important share. 



Upland swamps and ablation swamps do not depend to such a 

 degree on the presence of terrestrial water for their growth as 



