292 
SILURIA. 
[Chap. XII. 
in brackish-water bays or estuaries, in which large and predaceous Sauroid Fishes 
prevailed. 
The next zone, in ascending order, and in which lie some of the most productive 
coal-fields of Scotland, is, on the contrary, one of purely marine character, in respect 
to its fossil -bearing limestones, since all these calcareous beds, which alternate 
with coal, shale, and sandstone, are charged with the Sea-shells of the Mountain 
or Carboniferous Limestone ; for, as all these limestones (of which the Govern- 
ment Geologists Messrs. Howell and Geikie * have mapped eight distinct beds 
in Mid- and East Lothian) are laden with well-known Producti, Bellerophons, 
Orthoceratites, and other Mountain-limestone types, the true geological horizon 
of this part of the great Scottish coal-field is absolutely determined, being mani- 
festly older than the chief productive overlying coal-fields of England. 
A general conception of the most productive Scottish coal-fields may be gleaned 
from an inspection of the section (p. 161) representing the order of the geological 
series in the western parts of Lanarkshire t- There, in proceeding upwards from 
the Upper Silurian rocks and Old Red Sandstone, the succession is admirably 
exposed on the sides of the brooks which descend from the higher moorlands. 
In these ravines the student sees, exposed to day, the manner in which several 
bands of limestone, charged with Producti and various other fossils, alternate 
with shales replete with Plants, and seams of coal, as well as with courses of the 
celebrated carbonaceous iron-ore known as the ( Black Band 'J. 
In the border tracts between England and Scotland we have yet to ascertain 
the extent to which the Coal-field of Canoby in Cumberland may be prolonged 
under the red sandstones, breccias, and Conglomerates of Permian age in Dum- 
friesshire. In Ayrshire, indeed, from beneath those red Permian sandstones 
which will subsequently be described, there rises a true Upper Coal-field, with 
the underlying limestones and sandstones. Again, in the basin of the Clyde, as 
well as in the Dalkeith and Fife Coal-fields, the same upper series is separated 
from the older zone of the limestones by a representative of the Millstone-grit, 
on which it rests. 
Mr. Geikie has favoured me with the following description of the Carboni- 
ferous series in the parts of Scotland which he has surveyed : — 
"In Berwickshire, and northwards through East Lothian to the Ochil Hills, the 
upper red and yellow members of the Old Red Sandstone are found to graduate 
upward into the base of the Carboniferous series. In the western districts of Scotland, 
on the contrary, that series seems, at least in wide areas, to have no determinate base, 
but to lie unconformably on older formations. Arranged in descending order, the fol- 
lowing tabular grouping of the Scottish Carboniferous rocks has been made out : — 
* As Director-General of the Geological Survey 
of the British Isles, it is my duty to explain that 
the boundaries, subdivisions, and details of the 
Carboniferous masses, and their relations to Silu- 
rian, Old Eed, and igneous rocks in the counties of 
Edinburgh, Haddington, and Fife, or around the 
Scottish metropolis, were first defined upon the 
six-inch maps, and are now published on the usual 
one-inch scale. The Officers of the Geological 
Survey have delineated with precision the relations 
of all the trappean or igneous rocks, so rife in that 
region of Scotland, whether they be the great co- 
temporaneous felspathic agglomerates and fel- 
stones which are splendidly exhibited in the coast- 
cliffs between North Berwick and Dunbar, or the 
numerous rocks of greenstone and basalt which, 
in the Lothians or in Fife, have been subsequently 
intruded among the Carboniferous strata. The 
reader who desires to understand how these ig- 
neous operations have been in play during recent 
geological times should consult a section drawn 
by Mr. Geikie across the well-known hill of Ar- 
thur's Seat at Edinburgh, as published at the foot 
of the Geological Map of Scotland by that author 
and myself. Even whilst I write, Mr. Geikie is 
about to show that the last great eruption of ig- 
neous rocks in Scotland took place after the for- 
mation of the Middle Tertiary or Miocene depo- 
sits. In 1858 the Eev. T. Brown transmitted to me 
a valuable detailed section along the south coast of 
Fife, showing the vast thickness of the inferior se- 
ries of sandstones and shale with eight calcareous 
courses and five beds of the ordinary Carboni- 
ferous or Productus limestone, the whole being in 
great undulations, with many protrusions of ig- 
neous rock. The details are published in the 
Quart. J ourn. Geol. Soc. vol. xv. p. 59. 
t See also Page's Advanced Text-Book of Geo- 
logy, p. 137. 
I See my memoir ' On the Silurian and Lower 
CarboniferousRocks of Lesmahago,' in the Journal 
of the Geological Society, vol. xii. p. 15, &c. 
