464 R. HARKNESS AND H. A. NICHOLSON ON THE STRATA BETWEEN
Ci/bele verrucosa, fflomus Bowmanni, and Lichas laxatus, can leave no
doubt as to the correctness of the inference that these rocks belong to
the Bala or Caradoc age. The presence of what appear to be unequi-
vocal ashes which contain some of these fossils high up in the series at
Swindale also deserves attention as showing that the volcanic forces
which gave rise to the ashes and lavas of the Borrowdale group still
maintained an intermittent activity during the deposition of the
Dufton Shales. There would thus appear to have been no break of
continuity between these shales and the underlying Borrowdale
rocks — a conclusion which is further borne out by the substantial
identity between the fossils of the Dufton Shales and those of the
Style-End Grassing beds.
The annexed section (fig. 1) exhibits the stratigraphical relations
of the Dufton Shales in Swindale Beck, where, as before stated,
they are very well exposed.
Fis. 1.-
-JT.INTJE
-Sketch Section of the Strata in Swindale Beck, near Knock.
(Length rather more than half a mile.)
s.sw
a. Ashes belonging to the Borrowdale series
c. Coniston Limestone.
e. Knock beds (green and purple slates).
/. Black flags with Monographs colon us, Barr., probably Coniston Flags.
b. Dufton Shales.
d. Graptolitic mudstones.
2. Coniston Limestone.
The " Coniston Limestone," notwithstanding its comparatively
small vertical extent, has long occupied the position of being the
best-defined and most universally recognized of all the divisions of
the Lower Silurian series of the north of England — a position which
it owes to its easily recognized lithological characters, and to the
number of organic remains which it has yielded. It is unnecessary
here to recapitulate the geographical range of the Coniston Lime-
stone. Its main line of outcrop crosses the Lake-district in a direc-
tion from S.W. to X.E., running from Millom on the one hand to
Snap Wells on the other. It is more or less developed in Raven-
stonedale,Dentdale. the Sedbergh valley, near Ingleton, in Ribblesdale,
at Ireleth, at High Haulme. in Furness. and at various points in
the Lower Silurians which lie to the south-west of the Cross-Fell
range.
Lithologieally the term " Coniston Limestone is somewhat mis-
leading, as it is never wholly calcareous in its composition, and the
calcareous element is occasionally almost wanting. In its most
typical form, as seen in its range between Long Sleddale and