158 
SILUEIA. 
[Chap. VIII. 
the Old Bed and Carboniferous deposits, there is no evidence in that tract 
of a younger order of things beyond what may be viewed as a transition 
from the Lower to the Upper Silurian. 
On the opposite side of the South- Scottish axis, however, the highly 
convoluted strata which form the southern headlands of Kirkcudbright 
Bay (Balmae Head" and Little Boss), and the rocks on the east side of the 
Bay, are, judging from their fossil contents, of the age of the Wenloek 
shale. Hard and intractable as the Ireleth slates of Cumberland, which 
have been placed on the same parallel, and containing only very rarely 
nodules slightly calcareous, these argillaceous and siliceous schists have 
yielded a good many fossils. In them we find, it is true, the Lower Silu- 
rian forms, such as Orthoceras tenuicinctum (Chap. IX.) and Leptsena 
sericea ; but from the same beds Mr. Salter has catalogued the following 
Upper Silurian types : — Bhacops caudatus, Beyrichia tuberculata ?, Ortho- 
ceras annulatum, Chonetes lata, Bhynchonella nucula, Bterinea lineatula, 
Grammysia cingulata. With these are associated other fossils, which per- 
vade nearly the whole system, such as Atrypa reticularis, Halysites cate- 
nularius, Graptolithus priodon, and Bellerophon trilobatus. The last fossil, 
which in England occurs in the uppermost Ludlow rocks, is associated, 
in Ireland, with lower types. 
In this way we have no means of defining, with greater precision, the 
age of the fossil-bearing promontories of Kirkcudbright than by saying 
that they overlie the great mass of the older Silurians, and contain a 
younger fauna. They appear, in short, to be more referable to the Wen- 
lock than to the Ludlow formation. Through the discovery of the upper- 
most Silurian rocks in Lanarkshire (which are about to be mentioned), it 
might rationally be surmised that the time was when there existed also 
on the southern side of the Dumfries axis, a large and visible upward de- 
velopment of the youngest Silurian rocks, which ranged from the south 
of Scotland to meet the equivalents of the Wenloek and Ludlow rocks of 
the Cumbrian or Lake district of England — all which deposits are now 
concealed beneath the sea. 
But on the immediate shore of the Bay of Kirkcudbright, all such links 
have been omitted ; for there the lower part of the Upper Silurian series, 
as just described, is at once unconformably overlain by strata of the Car- 
boniferous era*. 
* The phenomenon of the unconformable super- upper beds being conglomerates and coarse sand- 
position of the Carboniferous strata (with Moun- stones. Professor Mcol and myself examined 
tain-limestone fossils &c.) to the Silurian rocks, Balmae Head in 1851. Mr. Stevenson described, 
along the coast of the parish of Kerrick, in Kirk- the nodular shale of Little Eoss Head, Ed. N. 
cudbright, has been described in detail by Mr. Phil. Journ. vol. xxxv. The organic remains above 
Harkness, in a memoir read before the Geological alluded to were collected by the Earl of Selkirk 
Society, April 1853. This author explains by sec- and Mr. Fleming. After describing the rocks of 
tions the extreme curvatures of all the rocks which this small island, and showing that they contained 
he considers to be Upper Silurian, and parts of Graptolites, both double and single, as well as 
which he shows to have been shore-deposits. He Orthoceratites, &c, Mr. T. Stevenson, the eminent 
further indicates the dykes of porphyry which engineer, correctly inferred, sixteen years ago, 
protrude, and has endeavoured to mark the line of that these strata were of Silurian age (Edinb. 
separation between the Lower and Upper Silurian, New Phil. Journ. July 1842). 
which on the whole rise up to the N.N.W., their 
