The Southwest Region - Southern England - page 50

FIG 47. China clay excavations at St Austell. (Copyright Dae Sasitorn & Adrian Warren/
www.lastrefuge.co.uk)
The older rocks surrounding each of the granite intrusions generally show evid-
ence of alteration that occurred as the mobile granite worked its way upwards from
below. This contactmetamorphism , often accompanied by the growth of new minerals,
is the result of the transfer of heat and introduction of new chemical components from
the granite. It has usually resulted in making the rocks more resistant to later erosion at
the surface.
Younger episodes
Sedimentary markers
Between 7 and 20 km to the southwest of Exeter, traversed by the A38 and A380
trunk roads, the Great and Little Haldon Hills are capped by a layer of sediments, as-
signed to the Upper Greensand, and spanning in age the Early/Late Cretaceous bound-
ary (between about 105 and 95 million years ago). These are the westernmost erosional
relicts of a continuous sheet of sediment of this age that extended across much of the
rest of Southern England. In the Haldon Hills area, the sandy and fossiliferous material
seems to have formed near the coastal margin of an extensive Cretaceous sea.
The Haldon Gravels are distinctive deposits that occur above these Cretaceous
sediments. They consist largely of flint pebbles and contain sand and mud between
the pebbles. Some of the gravels appear to be the result of removal by solution of the