130 
Helton Moor beds. The lecturer had previously indicated the 
possibility of such a discovery being made.* 
Strictly speaking, no true limestones of Silurian age occur in 
Cumberland and Westmorland. ‘There is, however, a calcareous 
band at the very base of the Silurians in eastern Westmorland, that 
corresponds to the Pentamerus Beds of Wales. Calcareous concre- 
tions, often aggregated together in sufficient quantity to be almost 
entitled to be described as limestones, also occur here and there 
on various horizons in the Silurian rocks. Some of the lower of 
these must represent, in time, the well-known Dudley Limestone ; 
while the higher concretionary zones must correspond with that of 
Aymestry. 
Above the Silurian rocks occurs the greatest unconformity 
known in the whole geological series: a thickness of not less than 
five miles of strata being absent in places between the Older- 
Paleozoic rocks and the succeeding rocks of Carboniferous age. 
Part of this gap—but only a small part—is filled up by the Middle 
or Caledoniant Old Red, which in central Scotland consists of a 
vast thickness—many thousands of feet—of conglomerates and 
sandstones, with volcanic rocks in their higher parts. The whole 
series lies unconformably upon all the older rocks ; so it is probable 
that the greater part of the unconformity traceable in Cumberland 
may date from times posterior to the highest of the Silurians, but 
anterior to the deposition of the Caledonian Old Red. There are 
reasons for believing that the Caledonian Old Red, or the higher 
members of that series, formerly covered the Lake District; and 
that it included some (possibly thin) beds of émestonet The 
* «7 think it quite possible that, in some areas [referring to the north of the 
Lake District] beds even low down in the Skidda Slate series might be directly 
surmounted by the equivalents of the Coniston Limestone.”-—/Pvoc. Geol. 
Association, Vol. 1X. No. 7, p. 9 of Reprint. 
+The lecturer proposed this as a convenient designation for the ‘‘Old Red” 
which is unconformable to the Silurians on the one hand and to the true, or 
Upper, Old Red, on the other ; thereby confining the term ‘‘ Lower Old Red 
Sandstone” to that group which graduates downward into the Ludlow rocks. 
+ These may have been of marine origin, and therefore equivalent to the 
limestones of the Devonian rocks. 
