C. L. Walton 
Near the western edge the plateau rises from a longitudinal (n. and 
s.) valley occupied by sections or tributaries of the Rheidol, Ystwyth 
and Teify to a small watershed, running from North to South. This 
has the feeders of the longitudinal valley on its Eastern side and the 
torrent streams of the plateau edge on its Western. 
The watershed is pierced in several places by plateau edge streams 
which have “cut back,” but in the North, where the longitudinal valley 
is slight, and the large area of high plateau rises quickly to Plvnlymon, 
there is, along the watershed, a series of lakes between 900 and 1400 
feet above sea. Most of these have been utilised and altered in connec¬ 
tion with the formerly very extensive lead mining operations, while 
“leets” conducting water from these lakes mark the hillsides in all 
directions as also do the remains of the numerous spoil heaps and ruins 
of former mine buildings. The deleterious effects of these lead workings 
upon stock, crops and fisheries within the Area is being dealt with 
by others, and will merely be mentioned here as a distinctly adverse 
factor on the general Biology of the Area. This High Plateau is the 
great summer grazing area for sheep. The fall line or slope between 
this High Plateau and the lower Coastal Plateau is of considerable 
extent and importance and includes much of the woodlands of the Area; 
the land is frequently rough and ill drained, and the numerous streams 
often occupy deep ravines or cwms. The Coastal Plateau is almost 
entirely composed of the “Aberystwyth Grits” of Silurian age, and 
contains the best cultivated agricultural land within the Area; here 
also, naturally, is grouped the bulk of the population. 
The only town within the Survey Area is Aberystwyth, and the 
main mass of the population lies in its vicinity, although there is a 
considerable chain of villages lying along the main road from Aberyst¬ 
wyth to Machynlleth, namely Bow Street, Llanfihangel, Talybont (a 
large village), Taliesin, TreYddol, Eglwysfach, etc. 
The chief rivers are as follows: to the n.w. the Area is bounded for 
some distance by the estuarine portion of the River Dyfi, and flowing 
into this portion are several streams which, rising on the mountains, 
flow westward through steep rocky valleys until they reach the Dyfi 
Flats, whence, seaward, they now largely occupy artificial channels, 
considerably affected by tidal flow. The chief of these from n. to s. 
are, the streams that join and then occupy the Llyfnant valley; the 
Einion, Clettwr and Leri: this latter being longer than the rest and 
receiving a number of tributaries from the Cwm Ceulan, Cwm Ty-nant, 
etc. 
