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The Preston Guardian
Saturday 23 May 1863
Drift Deposits Near Burnley
By T.T.Wilkinson, F.R.A.S., &c., &c.
(From the Transctions of the Manchester Geological Society)
The drift deposits in the neighbourhood of Burnley, as well as those near Manchester, appear to possess several features of considerable importance, for, in addition to the usual clay and gravel, they contain pebbles and masses of foreign rocks, some of which are well water-worn, whilst others are so fresh and angular as to admit of scarcely any other explanation of their presence here than by iceberg-carriage from a great distance. Encouraged by what Mr. Binney has stated and done in p.p. 8, 9, and 351 of the third volume of the Transactions of this Society, and elsewhere, I beg to offer a few remarks on those deposits which have recently fallen under my own observation.
A little east of the Four Lane Ends, near Blackburn, 650 feet above the level of the sea, the drift immediately overlies the Rough Rock, which crops out above the Corporation Park, at an angle of about 75°. On the crest of this hill the blue clay, from which bricks have recently been made, lies upon the surface. It is, however, too much intermixed with sand from the disintegration of the rock to form good bricks. The pebbles and boulders contained in the clay appear mostly to belong to the carboniferous formations, and their water-worn appearance indicates long-continued denuding action by water. Both limeston and gannister pebbles occur in abundance, the former of which must have been drifted from a considerable distance.
Extensive deposits of yellowish sand occur opposite Portfield, near Whalley, 196 feet above the level of the sea; at Whittle Field, near Burnley, 451 feet above the level of the sea; and also at Healey Hall, on the slope of Burnley Moor, 580 feet above the level of the sea, masses, or veins, of hard carbonaceous matter are occasionally found in this sand, probably indicating the remains of former vegetation; but I have not yet been fortunate enough to detect any shells in these deposits.
At the Quarry, near Habergham Hall, the sandstone rock immediately overlies the Dandy Bed of the Burnley coal-field. The surface of the rock is here covered with a coating of soft loamy shale, which soon passes into clay on exposure to the atmosphere. This shale is almost wholly composed of calamites, ferns, sigillaria, &c., indicating a profuse vegetation, which must have been covered by succeeding deposits in comparatively stagnant water. Above this shale there is a bed of dense blue clay, 22 feet thick, containing fragments of cannel, coal, &c., the debris of still higher strata. Rough rock and grit boulders, portions of encrinital limestone, sometimes water-worn, together with rounded sandstone and limestone pebbles, occur in abundance, imbedded in the clay, and the whole is surrounded by the remains of the denuded rocks which once occupied the next position in ascending order.
In the quarries, near Sandy Gate, Habergham Eaves, 462 feet above the level of the sea, the drift is from 30 to 50 feet deep. It consists of dense blue clay at the bottom, and gradually passes into dark brown near the top. Large boulders of sandstone, similar to that which lies beneath, occur in these deposits, few of which appear to have suffered from the action of water. From their positions in the clay it may readily be inferred that they may have fallen from the faces of the cliffs which then probably bordered the ancient seas. Portions of encrinital limestone also occur; and there is no lack of rounded fragments of cannel, together with sandstone, gannister, and limestone pebbles.
In similar drift at Swindon, about two miles east of Burnley, 800 feet above the level of the sea, and just under the Pennine chain, large boulders of new (?) red sandstone are occasionally found in connection with abundance of rounded limestone. In former times the farmers have washed the drift in Swindon valley, and have burnt the limestone thus obtained in kilns, the ruins of which still remain in several places.
During the formation of a main sewer in Trafalgar-street, Burnley (1862), the workmen found a large boulder of grey granite. It was firmly embedded in a yellowish clay at a depth of about 15 feet from the surface. Encrinital limestones were also plentiful in this cutting. These deposits overlie the Thin Mine of the Burnley top beds; the Cannel Bed, which is the next in ascending order, having apparently been washed away.
In various localities extensive pebble beds occur, indicating former beds of rivers, or the margins of ancient seas and lakes. Several of these bear evidences of powerful currents, which, from the set or inclination of the pebbles, appear to have flowed accross the country in a N.E. to S.W. direction. This is very evident from an examination of the inclination of the debris in most of the sections previously noticed, but especially in one, which exposes a portion of the grit series between Haslingden and Helmshore. This inclination of the stones found in pebble beds, and drift deposits generally, appears to me to be capable of affording more information to gelogists respecting currents, &c., than has yet been noted; and hence I would suggest more attention to this circumstance from observers than has yet been bestowed upon it. Prior to the upheaval of the Pennine chain a broad strait must have stretched across portions of Lancashire, Yorkshire, Durham, and perhaps Northumberland, thus connecting the present German and Irish seas; and the current thought this strait must have run from N.E. to S.W., as indicated by the inclination os the pebbles and boulders in these drift deposits. Portions of floating icebergs from the north of Scotland broken off from the edges of the glaciers and charged with portions of granite and the older rocks, would then find their way down this channel, and becoming stranded in the shallow bays, would drop their cargoes of boulders among the silt at the bottom of the turbid waters. Red sandstone boulders might, perhaps, be drifted in a similar manner from the neighbourhood of the Tees, or from the cliffs of what is now the Vale of York. Encrinital limestone, not water-worn, might also be transported from the north by the same mode of iceberg-carriage, to the deposits in which they are now found. Or again, if we adopt Sir Charles Lyell's and Mr. Hull's conceptions, the same results would evidently be obtained.
On the gradual upheaval of the Pennine chain, the sea would consequently retire, both on the eastern and western sides of the country, leaving behind it those significant terraces which may be seen on the slopes of the hills abutting on the valleys of the Calder, the Hodder, the Ribble, and the Irwell from about Ramsbottom to its various sources. The contents of these drift deposits also indicate several widely different conditions of things. There must have been many quiescent periods, and also many gradual depressions of the surface during the formation of the various coal-seams and the deposition of the rocks and shales by which they are overlaid. After the latest deposits there must have been a gradual upheaval, with occasional fractures, from the bed of a deep ocean, and, as the bottom came nearer the surface, the more powerful would be the currents, and hence the variable, but extensive, denuding action of water which is apparent everywhere.
There is, however, good evidence that within the historic period the coast of Lancashire, at least, has again undergone considerable depression. In the times of the Romans there was probably no estuary of the Mersey. Ptolerny does not include this now important opening in his topography of the coast. The dredging operations at Liverpool continually afford prrofs of recent land surface; and oven hazel branches, containing nuts, were dug up for a considerable depth during the formation of the Sandon Dock. Along the shore from near Formby towards Preston, there are the remains of an extensive ancient forest. Many trunks of trees were exposed during the formation of the East Lancashire Railway, and are still to be seen in the pools on each side of the road. The roots of these are mostly below high-water mark, and in some places the trunks extend into the sea; but all of these must originally have flourished at a much higher elevation. About Southport they are so numerous that they have been used to form ornamental fences for some of the gardens.
At Blackpool, and on towards Fleetwood, the sea is washing down the cliffs at the rate of about one yard in breadth per annum; and tradition states, one very probable grounds, that nearly half a mile in breadth of this part of the Lancashire coast has disappeared within the last hundred and fifty years. There are, therefore, strong reasons for supposing that Lancashire is at present undergoing a gradual depression. In Scotland, on the contrary, according to Mr. Goikie, the reverse operation is in progress, and it may form an interesting subject for some speculative mathematical geologist to enquire whether this apparent flexibility of the earth''s crust is due to internal local action, irregularly applied, or whether it is the natural result of those mechanical laws which govern the earth when considered as a comparatively solid film resting upon a fluid interior.
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Mel
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