IO PROCEEDINGS COTTESWOLD CLUB 1904 
dislocation which runs from Lilleshall in a south-westerly 
direction into South Wales. At intervals on this latter 
line of fault appear narrow ridges of Archzean rocks, chiefly 
Uriconian. The most important of these masses are the 
Wrekin chain, near Wellington, and the Caer Caradoc 
group of hills at Church Stretton. These ridges are 
wedges of the Archzan floor thrust up through younger 
strata, and in some localities they further resemble the 
Malvern chain in that they are faulted against Cambrian 
and Silurian rocks on one side, and Triassic strata on the 
other. 
The Uriconian rocks of Shropshire indicate active vul- 
canism. Lava-flows, often of great thickness, alternate 
with beds of ashes, which vary between coarse breccias 
and fine dust. But in this area we have clearer evidence 
of the conditions under which the rocks were formed. 
Some of the eruptions appear to have taken place on the 
land, for in Caer Caradoc the felsite contains geodes 
of quartz, which show a tendency to lie in parallel planes, 
as if they had replaced air-bubbles in a lava-flow. But 
a large proportion of the Shropshire Uriconian was 
deposited under water. The bits of felspar and pitchstone 
which make up a considerable proportion of the ash-beds 
are often water-worn, and rounded grains of quartz are 
commonly present. Still more emphatic evidence is fur- 
nished by frequent beds of conglomerate, interstratified 
with the finer bands of ash. They contain fragments 
up to six and eight inches in diameter, often as well 
rounded as the pebbles on a storm-beaten shore. The 
predominant materials are quartz, granite, several forms of 
gneiss, mica-schist, quartzite, felsite, pitchstone, and altered 
grits. The felsite and pitchstone are similar to Uriconian 
lavas, and are probably the result of contemporaneous 
denudation ; but the others are derived from pre-existing 
land. Some of them are common Malvernian types; the 
