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The Quarterly journal of the Geological Society of London (12684285213)
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150
PROCEEDINGS OF THE GEOLOGICAL SOCIETY. .Feb. 25,
After these remarks, we are at once prepared to compare the rocks
developed in the great transverse sections of the "Welsh and Cumbrian
mountains. The lower Cambrian groups (Bangor and Festiniog,
Nos. 1 and 2 tabular view) are amply represented by the green slates
and porphyries of Cumberland. The upper Cambrian groups (Bala and
Caradoc, Nos. 3 and 4) are (however imperfectly in thickness) clearly
Diagram illustrating the Comparative Development of the Silurian
and Cambrian Rocks in Wales and Cumbria, respectively,
Cambria. Cumbria.
Upper PALiEozoic
Middle PALiEozoic,
Ludlow
Wenlock
Caradoc . .
Upper Bala ...
Bala Limestone
/Carboniferous Lime-
l stone.
Old Red Sandstone.
Kirkby flags.
Coarse slates.
Ireleth slates.
Coniston grits.
, . Coniston flagstone.
. Coniston limestone.
Lower Bala
Slates and porphyry*
Arenig slates and por- &:
phyry....
Tremadoc slates . .
Lingula flags
Harlech grits
Llanberris slates . . ,
Metamorphic
Granite
. SMddaw slates.
Metamorphic.
Granite.
represented by the Coniston limestone, flagstone, and the hard coarse
grits of the Westmoreland sections.
The equivalents, in the North of England, of the Wenlock and
Ludlow groups (Nos. 5 and 6) have already been noticed. Using the
words "Silurian System " in any definite sense, these are the groups
which truly and exclusively belong to it as a system ; for the Caradoc
the characteristic Wenlock species ; while the so-called Caradoc sandstone of May
Hill contains the Wenlock fossils in abundance, and none of the characteristic
Cambrian types. But is there a single section in which these two distinct groups
of fossils appear together in one stage ? If no such section can be found, why may
we not suppose that the Caradoc sandstone of May Hill is a group superior to the
Caradoc sandstone of Horderley ? Should we ever be able to answer this question
in the afBrmative, the ambiguity alluded to in the text would be at an end. The
statement here given is drawn from the fossil evidence supplied by the Cambridge
Museum,
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