The Woodlands of England. 123 
species are absent from the alder-willow thickets which occur on 
soils fed with neutral or acidic waters. In the eastern portions of 
the New Forest, especially between Lyndhurst and Beaulieu, close 
thickets of the latter type are striking features of the landscape, as 
they follow, sometimes discontinuously, the courses of the streams 
across the sterile soils of the Calluna-heath. In some places, 
they form a narrow fringe on the river alluvium ; while in other 
cases, they appear as extended islands enclosed within the valley 
peat moors which have arisen subsequently to the woods as a 
consequence of stagnation of the ground water. Within these 
gloomy thickets, heavy with moisture, grows a rank vegetation 
allied to that of marshes and almost hiding the numerous rotting 
trunks of fallen trees. In the course of time, as a result probably 
of decreasing aeration of the soil, the marshy vegetation gains the 
upper hand: the former woodland becomes submerged, and leaves 
only a sub-fossil tree-layer in the peat of the newly formed moor. 
In the Furness district of north Lancashire and in the adjacent 
parts of Westmorland, alder-willow thickets of a similar character 
appear on the margins of the lowland peat moors, where the “ moss” 
abuts on the “ hard land.” Here, above estuarine silt deposited in 
the long, narrow, tidal inlets, extensive peat moors have grown. 
On their edges, the drainage from the upland has been impeded]; 
and the natural woods consequently belong to this series. As the 
level of the peat rises, the soil of the alder thickets encroaches on 
the adjoining oakwoods, whose ground vegetation gradually gives 
place to the advancing wet moorland associations. 
Of a different nature, and arising subsequently to the deposition 
of the peat, are the “carrs” of the Norfolk fens. These may be 
subdivided into fringing carrs which line the banks of some of the 
“ broads,” and fen-carrs which occur on older peat. Alder and 
Salix cinerea are abundant in both types. Species of Ribes are 
abundant in the former; while Salix repens, Myrica Gale, Rhamnus 
Frangula,R. catharticus, Viburnum Opulus, and Ligustrum vulgare are 
characteristic of the latter. Quercus Robur ( =Q . pedunculata) 
occurs in both, but not as a dominant tree. Caltha palustris, Spircea 
Ulmaria, Iris Pseudacorus, and Carex paludosa are abundant in the 
fringing carrs, but they seldom or never flower. The rest of the 
ground vegetation of both types of carr is composed of fen-inhabiting 
species. 
Alder-willow thickets, as they are developed in other parts of 
