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The Taunton Rock
Trail
The science of geology
has been built upon the study of rocks. Hence, we recommend as a first
step, a short tour of the building stones that can be seen close to the
County Museum. Here we concentrate mainly on what the stones look like
as this is the basis for understanding them. More details of the stones
are provided in Appendices B and D and the index. An * indicates a reference
in the glossary. A x10 hand lens will reveal finer details of the rocks..
The trail starts at
the entrance to the County Museum. The locations are numbered and shown
on the street plan Figure 12.1 . Please check the opening hours of the
Museum and its courtyard. The Museum has a bookshop and various displays
with a geological connotation. The booklet about Taunton Castle by Bush
(1988) is recommended. The Trail can be undertaken in less than two hours.
ACCESS FOR THE DISABLED
The trail crosses no roads and uses paths. Pass through Castle Bow into
Fore Street in order to avoid steps by Winchester House.
1. Driveway - Study
the stones in the walls driveway.
The wall on the left
is composed of a hard, siliceous, massive, crystalline rock varying from
grey to brown in colour. Contrast the smooth broken surfaces with the
rougher, weathered outer surfaces.
UPPER GREENSAND CHERT
2. Gateway - Locate
the stones on the left-hand wall in front of the gate with the help of
Figure 12.3.
HHS Yellowish-brown
mass of broken shell debris cemented with calcium carbonate and limonite
(hydrous oxide of iron); the latter gives the stone its golden colour
The short, sloping beds of irregular thickness are examples of cross-bedding*
where weathering has picked out the weaker beds - HAM HILL STONE
P-T S Red sandstone
with a variety of rounded and angular quartz sand grains. Iron oxide (haematite)
gives the red colour. Some blocks have a few small pebbles - PERMO-TRIASSIC
SANDSTONE
P-T B Red sandstone
with angular rocks/ fragments - PERMO-TRIASSIC BRECCIA
Step back and note
the use of the various stones higher up in the front of the Gateway including
the Ham Hill Stone shield (c1495). Proceed through to the Museum courtyard
if open.
3. Inner ward
The wall immediately
on the left consists of grey, calcareous* mudstones, with traces of horizontal
and wavy, laminations. Some weathered surfaces tend to be yellow as a
result of the oxidation of iron compounds. The grey colours indicate iron
in its reduced state. The stones are flaking badly. The many parallel
vertical cracks indicate that the rock has been stressed at some time
in the geological past. Some blocks contain the small fossil brachiopod*
Calcirhynchia calcaria. Please resist the temptation to remove these fossils.
BLUE LIAS
The yellow stones
in the parking area are mainly water worn, or frost-chipped, flints.
VALLEY GRAVEL
Lord Harding is mounted
on a plinth of a stone composed of ooliths* and shell fragments set in
a calcareous matrix*.
PORTLAND STONE
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