Geoscience Reference
In-Depth Information
FIG
235.
Looking northeastwards across Cambridge. (Copyright London Aerial Photo
Library)
Having looked at aspects of the histories of the main rivers, we now consider the
pattern of slopes in the three sub-areas identified in Figure 231, all of which include
this Landscape.
Southeast of the valleys of the rivers Rhee (or Ashwell Cam) and the lower Cam,
the slopes of the Chalk hills are well defined, particularly west of the Royston area
(Fig. 237,
c1
). Most of the steeper slopes in the outer or northwestern face of the Chalk
hills are the direct result of the presence of erosionally resistant (hard) layers in the
Chalk succession (see Landscape C for further details).
Southeast of these outer Chalk hills, the tops of the inner hills are largely underlain
by upper (younger) levels in the Chalk, and they tend to have the form of a tilted plat-
eau sloping very gently to the southeast. Much of this tilted plateau has a cover of Qua-
ternary deposits, mainly those left by the Anglian ice. Many of the local valley slopes
are capped by this material. The slopes, therefore, have probably been eroded during
the last 400,000 years since the deposits were left by the Anglian ice sheets.
FIG
236.
The Cambridge Backs and the River Cam, with Clare and King's Colleges in the
foreground.
In the northern half of sub-area I, between Grafham Water (
b1
) and Harlton (
b10
),
the scenery eroded into the mudstone bedrock consists of well-developed tributary val-
leys separated by narrow, often near-parallel ridges. The ridges are generally capped by
a sheet of Quaternary (Anglian) ice-laid material. Similar uplands, with clearly defined
tributaries and valley slopes carved into Anglian ice-laid material and Late Jurassic
mudstones, occur north of the Ouse near Huntingdon (
b2
) and east of the Ouse near
St Neots (
b6
), where they make up part of the 'Western Plateau' of Cambridge. Cen-
tral parts of the plateau are about 70 m above sea level. Below its surface, its cover
