CHAPTER VI 
MARSH AND AQUATIC ASSOCIATIONS 
General distribution of the marsh (or swamp) and aquatic associations. 
Non-calcareous waters. Swamps on the sandstones and shales. Cal- 
careous waters. Swamps on the limestone. Ruderal marsh species. 
Reed swamps. The vegetation of quickly flowing streams. Alien 
aquatic plants. The relation of mineral salts to the flora and 
vegetation. 
GENERAL DISTRIBUTION OF THE MARSH (OR SWAMP) 
AND AQUATIC ASSOCIATIONS 
In the Peak District, as on the Pennines generally, aquatic 
and marsh associations, and more especially the former, are 
very meagrely represented. The Pennines, consisting of 
fissured rocks like the Carboniferous sandstones, and porous 
rocks like the Carboniferous limestone, have no natural lake- 
lets or tarns such as occur on the older Silurian and Cambrian 
rocks, Again, in the Peak District, there are no extensive 
alluvial flats; and it is in such situations that aquatic and 
marsh associations attain a maximum degree of development. 
From such lowland alluvial deposits, some of the more cosmo- 
politan aquatic and marsh plants spread up the streams, where 
they form narrow, fringing associations which are too small, 
however, to be marked on vegetation maps except such as are 
constructed on a very large scale. Hence aquatic associations 
and reed swamps are poorly developed and only of local 
occurrence on the Pennines. 
In this district, marshes or swamps are characteristic of 
those spots on the hill-slopes where springs issue, and of the 
immediate banks of the streams where these banks happen to 
be flat. Reed swamps are very local; and even when they 
do occur, they are very small and not very typical. The streams 
themselves are tenanted by numerous characteristic mosses, 
