450 
and Scotland on the one hand, and to the east of the latter 
country on the other, as significant of a denudation earlier than 
that of the sea which has in later times divided the British Isles. 
Another epoch of carth-movements closed—as was to be expected 
—the Carbonilerous subsidence and deposition. We trace one 
line of flexures and of intens: compression along a broad 
zone, including the south of England, from Germany to Ireland ; | 
another less intense over the northern part of our country ; the 
axes of the former flexure striking a little north of west, of the 
latter about west-south-west. The one appears to me to indicate 
a thrust from a great mass of hard, more or less crystalline rock 
in the south, which probably led to the formation of a mountain- 
chain extending from North-Central Europe over the Channel to 
the southern margin of England. The latter may be explained 
by the presence of th: above-named north-western continent. 
In the Perauan time terrestrial conditions probably prevailed 
over a large partof Britain. It is extremely difficult to ascertain 
the exact circumstances under which the Permian beds of Cen- 
tral England were deposited, but I should thiak they imply a 
return to physical conditions not unlike those of the Old Red 
Sandstone, though perhaps the marine fossils which have been | 
found in Warwickshire may indicate that the water there had | 
some imperfect connection with the sea. I must not discuss the 
vexed question of the age of the Pennine Chain, but must con- 
tent myself with expressing my opinion that, at most, it can 
only, as yet, have very partially interrupted the continuity of the 
water in Northern England. The beds there appear to indicate 
a supply of materials from the north and north-west, as if the 
old rivers had not been wholly diverted by the great earth-move- 
ments which closed the Carboniferous period. Sir A. Ramsay’s 
view, that the water in which the dolomitic limestone was de- 
posited was more or less cut off from the open sea, seems to me 
by no means improbable ; in any case, it is a rather exceptional 
formation, and over the greater part of Britain, probably, land 
sculpture continued, and deposition was on the whole local. 
With the Trias a new era commences ; physical features had 
been now produced, which in all probability endured through a 
considerable part of Mesozoic times. The facts which I have 
laid before you, regarded in the light of the general principles 
indicated above, compel us to look away from the immediate 
vicinity for the bulk of the materials, coarse and fine, of which 
the northern ‘lrias is composed, though neighbouring hills may 
have furnished occasional contributions, especially to the earlier 
deposits. The analogy of the Old Red Sandstone, the Calciferous 
Sandstone of Scotland, and the Nagelflue and Molasse of Switzer- 
land, together with other peculiariti s too well known to need 
repetition, make it in the highest degree probable that the Bunter 
beds were not deposited in the ocean.! Hence they must be 
either deltas formed in an inland sea or in a lake, or true fluviatile 
deposits. Neither lake nor inland sea ap,ears likely to have been 
sufficiently large to admit of waves or currents capable of either 
rounding the pebbles or transporting the materials. We are 
therefore compelled to fall back upon the action of rivers. The 
sandy beds of the Bunter indicate a stream flowing from one- 
third to half a mile an hour, the pebbles one from two to three 
miles; that is to say, the Upper and Lower Bunter sandstones 
would require the former rate of movement, the Pebble Beds the 
latter. Now, we must remember that, in the West-Central dis- 
trict, the Lower Trias consists of three wedge-like masses, about 
a hundred wiles in length, of which the coarser is probably the 
more extensive. ‘The comparative uniformity of the deposits in 
each case indicates a uniformity of flow, and suggests either a 
large and broad stream, not liable to much variation, or one 
which, when flooded, quickly made a channel of its valley, and 
deposited mainly at such season. I have the greatest difficulty 
in understanding how a current of the requisite velocity could be 
maintained by the water of a river or rivers flowing into a lake 
or an inland sea, or in explaining the tripartite arrangement of 
the beds on the hypothesis that a basin was gradually filled up from 
the northward by astream which, like the Rhone at the upper end 
of the Lake of Geneva, gradually advanced its delta by flowing 
over the materials which it had previously deposited in the basin. 
Hence I believe that we must regard the Bunter beds as sub- 
aerial deltas, analogous to the conglomerates in the Siwalik 
deposits of India, and to the sandstone and nagelflue on the 
1 Compare also the Bunter and Keuper in the region traversed by the 
German Rhine. 
2 The analogy of the Indian conglomerates was suggested to me by Dr. 
Blanford. See Geol. Mag. Dec. 2, vol. x. p. 514. 
NATURE 
| insulated like the Caspian. 
| rivers. 
[Sept. 9, of 
outer zone of the Alps, deposits in all respects very similar to the — 
English Bunter. We may suppose, then, that rivers emerging j 
on each side of the Pennine Chain from a mountain land first 
formed the Lower Bunter sandstones, then, owing to increasing . 
upheaval in the mountain district, and corresponding depression 
in the lowlands, flowed more swiftly so as to cover this deposit 
with the Pebble Bed, and lastly, as its former conditions returned, 
laid upon this the Upper sandstones. I have spoken, for the sake 
of clearness, as if these were perfectly distinct formations, but it 
would by no means follow that some part of the finer beds 
to the south-east might not be contemporaneous with a por- 
tion of the coarser beds to the north-west, as the velocity 
first increased, and then diminished. As I have already said, 
the materials of the pebbles and of the sand make it im- 
possible to refer the main constituents to local sources. 
Many of the rocks do not exist in the Midland; there is 
no reason to suppose that at that time there were in this region 
masses of land of sufficient area and height to feed important 
From currents of any other kind we are precluded, so 
that I believe we may safely turn our eyes northward and look 
for the ultimate source of the Triassic sandstones and conglo- 
merates among the older rocks of the Scotch highlands, and 
their extension to east and to west, though very probably the 
materials may have been more directly supplied from Old Red 
Sandstone and early Carboniferous strata, in remnants of which 
identical fragments may still be seen, In like way we may re- 
gard the Trias of the south of England as the detritus of at least 
one great river, which flowed from the west or south-west. The 
materials of the Keuper came from the same directions in each 
case, but here, I think, we have indications of deposition in an 
inland sea. Breccias formed on its coasts, and sands were at first 
deposited in it; but presently the area of water increased, and the 
coarser materials must have been arrested in the uplands, while 
the fine sediment which forms the marls may have been carried 
out into the salt lake and slowly settled down in its calm waters.? | 
Its shores may have been hardly more favourable to a vigorous 
development of life than were its salt-saturated waters; during 
this period and the preceding Bunter the lowland border of the 
mountains, like some of the northern districts of India, may have 
been arid and barren regions of shifting sands. 
The Trias of Northern Scotland very probably indicates a 
repetition on a more restricted scale of the physical conditions 
of the Old Red Sandstone, but after this we observe signs of an 
encroachment of the Atlantic on the above-named old area of | 
continental land. 
The Jurassic series is represented in Northern Scotland on 
both the western and eastern coasts by marine or estuarine beds. 
This probably indicates important modifications in the river 
channels, subsidence on the west altering the slopes, reducing 
the length, and cutting away some of the feeding-ground. Traces 
may still be discerned in England of the two northern rivers, 
but that which in Triassic times was the larger contributor, 
appears in Jurassic to have been gradually enfeebled ; the other 
one and the south-western stream seem to have still flowed with | 
some strength. Sands, however, now become comparatively 
local. Probably the coarser materials, as a rule, did not reach 
the sea. This appears at all times to have been comparatively 
shallow and inclosed by land on every side but the south-east. 
The recent discovery of Oxford Clay beneath the Cretaceous 
beds at Chatham suggests that a narrow strait running in a 
northerly direction may have insulated the Palzeozoic rocks 
| 
| 
T Tt may be useful to give a rough idea of the quantity of rock which must 
have been denuded in order to obtain materials for the Bunter beds. Sup- 
pose, for purposes of calculation, we consider the Bunter beds, whic 
cover the district from the Cheshire coast to the Midland counties, as forming 
the section of a cone contained by two planes drawn through the axis so 
as to include an angle of 30. If be the height of this axis, and ~ the 
ah Take, 
radius of the base, the volume of this figure is for purposes 
36 
of rough calculation, =} mile, »=80 miles, r= 3; the volume is abcut 
133 cubic miles. Conceive this piled up to form a long mound, in section an 
isosceles triangle x mile high, with a base of 4 miles. The length would 
be over 65 miles. Thus the materials buried in the Bunter beds of the above- 
named district represent a chain of hills unfurrowed by valleys sooo feet 
high, 4 miles wide, and 65 miles long. Suppose the Pebble Bed, a like 
slice of a cone, axis one-tenti of a mile, base 70 miles 4 the volume is more 
than 4o cubic miles. Suppose the quartz and quartzite pebbles one-tenth 
of its volume; these represent a mass of 4 cubic miles, or a line of hills 
like the above rooo feet high, 2 miles wide, and 20 long. 
2 The lake may have gradually become salt, or possibly the Muschelkalk 
sea may have for a short space invaded Britain, and then have been 
