444 HIND : CARBONIFEROUS ROCKS OF THE PENNINE SYSTEM. 
I make no attempt to correlate the various seams, though there 
can be little doubt that the Main limestone of Wensleydale is repre- 
sented by the great Limestone of Teesdale and Weardale, and possibly 
by the Dryburn Limestone of North Northumberland. 
At present there is little or no paleontological evidence to prove 
definitely that any life zones existed in the series, or to point out, with 
any certainty, the exact bed of limestone which corresponds to any 
definite band further south. The limestones become continually split 
up by masses of shale as they pass north, and many of them die out, 
and a correlation by the numerical position of a limestone as the series, 
counted either from below or from above, is bound to be incorrect. 
Mr. W. Gunn has attempted a precise correlation of the lime- 
stones of Dunbar and North Northumberland with the original 
Yoredale limestones, but it seems to me that the evidence for some 
of his assumptions is almost nil. The presence of an oil shale is re- 
garded as of prime importance as a stratigraphical line in Northumber- 
land and East of Scotland, but considering the great differences 
in the thickness of the purely sedimentary deposits in the two areas, 
it is not impossible that an oil shale was developed at a different period 
in the two fields. Oil shales are not unknown in the Edinburgh 
district at other horizons. The Oxford Limestone is stated to be 
the representative of the Hardraw Scar Limestone, and the Woodend 
and Dun Limestones are supposed to represent the Great Scar Lime- 
stone, but there is absolutely no evidence for such a correlation. 
In discussing the Carboniferous section at Dunbar, Mr. Gunn 
says : " Opposite Pinkhead . . . there is found an impure en- 
crinital limestone, which seems most probably to represent the Oxford. 
Thus nearly all the lower limestones are d3^ing out one after the other 
as we proceed westward, and at Skateraw most of the thin limestones 
between the Oxford and the Eelwell have disappeared, while at Gat 
Craig the lowest limestone is the Eelwell itself. Mr. Bennie, who 
has collected extensively both from the Acre limestone at Lowick 
and from the second limestone (counting from below) at Cat Craig, 
has come independently to the conclusion that these limestones are 
the same, because they attain a similar assemblage of fossils." * 
* Geol. Mag., Dec. IV., Vol. V., p. 347. 
