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ing for coal, that the actual Rock-salt, as a mineral, has been dug out from the mine. Before that time the chief supply was obtained from the brine springs of Droitwich, near Worcester. (Ansted.)
In the Marston mine, near Northwich, there are two thick beds of Rock-salt; the upper 84 to 90 feet, the lower 150 feet in thickness, and they are separated by 30 feet of indurated red clay containing strings of salt.
The Red marl is not a freshwater-bearing stratum. is necessary to penetrate it before an abundant supply of water is reached; and this is generally met with in underlying sandstones.
Mr. James Plant has given the following general section of the Upper Keuper Beds at Leicester :
a. Upper Keuper Marls, containing beds of gypsum and several thin bands of green marly sandstone, on which were found numerous pseudomorphous saltcrystals. 80 to 120 feet.
b. Thin sandy shales, with way-boards' of green marl. 25 to 30 feet.
c. Thick beds of soft white sandstone (water-stones).
20 to 30 feet.
d. Thin sandy shales, similar to b. 35 feet.
e. Red Clay.
The total thickness of the Keuper series near Leicester is from 700 to 1,000 feet. The water-stones are worked for building purposes.
The Red Marls are largely worked for brick-making near Nottingham.'
It is needless to indicate the particular geographical distribution of the Triassic rocks, as they can best be seen by
1 The Red Clay of Tuxford' belongs to the series.
reference to a geological map. They form part of the plain of York, and stretch through Nottinghamshire, Leicestershire, Derbyshire, Cheshire, Staffordshire, Warwickshire, Worcestershire, and Gloucestershire, and there is an outlying mass near Carlisle, consisting, according to the Rev. P. B. Brodie, of red marls and water-stones.
TRIASSIC ROCKS OF SOUTH WALES AND THE
In Glamorganshire, Gloucestershire, and in the neighbourhood of the Mendip Hills the Red Rocks consist of Dolomitic Conglomerate, Dolomitic Limestone, Sandstone (generally very calcareous), and Marl.
The Dolomitic Conglomerate, sometimes called 'Millstone' or 'Millgrit rock,' is an old beach deposit of Keuper age, derived chiefly from the Mountain Limestone. It rarely contains pebbles from the Old Red Sandstone, Millstone Grit, or Coal-measure Sandstones, partly because they are not so extensively exposed along the old margins, and partly because most of the sandstones would be of too friable a nature long to resist the friction to which they were subjected.
The included fragments are sometimes well-rounded, but often so slightly worn as to constitute, in fact, a breccia rather than a conglomerate. They vary in size, from that of a pea to boulders two or three feet in diameter; but stones about the size of a hen's egg constitute by far the larger proportion of fragments in the conglomerate. These are cemented together by the Carbonates of Lime and Magnesia, whence the name Dolomitic or Magnesian Conglomerate. Very frequently the cementing material is simply Carbonate of Lime, sometimes it is marl or ferruginous sand; the matrix is usually much coloured by peroxide of iron.
The thickness of the Conglomerate is subject to much variation it is rarely more than 30 feet.
The Dolomitic Conglomerate is sometimes burnt for lime. It is also used for building and ornamental purposes. The Draycot stone dug near Axbridge is well known in the district.
The Dolomitic Conglomerate usually occurs at the base of the Red Marl, and yet at the same time it occurs at all horizons along the margin of that deposit, where the beds dovetail one into the other, proving that its formation continued throughout the entire series. (See Fig. 8, p. 84.) Sandstones occur near Brislington, Chew Magna, and Yatton (Claverham or Clarham stone).
At East Harptree beds of chert are associated with the marls and conglomerates.
The remarkably even manner in which the Mountain Limestone has been denuded is well shown at Wallcombe, near Wells, where the Keuper beds rest on the basset edges of this rock. This even line is also very conspicuous in the vales near Frome.
The road to Wookey Hole on the one side of Wells, and that leading to Dulcot on the other, show in places in the Red Marl a bed called the 'Wonder Stone,' described by Messrs. Buckland and Conybeare as a beautiful breccia, consisting of yellow transparent crystals of carbonate of lime, disseminated through a dark red earthy dolomite.'
Beds of Dolomitic or Magnesian Limestone are conspicuous near Clevedon, and on the Glamorganshire coast.
Red and brown oxides of iron are not uncommon in the Dolomitic conglomerates, and they have been worked in many places, as at Llantrissant in Glamorganshire, on the Mendip Hills, &c. Reddle has been largely dug near
In the Dolomitic Conglomerate of Durdham Down, near
Bristol, some Dinosaurian remains have been found, which belong to the genera Palæosaurus and Thecodontosaurus.
The New Red rocks of West Somersetshire and Devonshire comprise a series of Marls, Sandstones, Conglomerates, and Breccias.
These different lithological divisions are in one sense inconstant, because each modification may occur anywhere in the series; but looked at in a large way, and as indicated in the coast-section between Axmouth and Teignmouth, the following order of succession seems applicable to the country between Porlock, Taunton, and the shores of the English Channel-the classification and thicknesses are taken from a paper by Mr. W. A. E. Ussher:
3. Conglomerates or Pebble-beds
2. Lower Marls.
1. Lower Sandstones and Breccias
Thus the Marls (5) sometimes contain beds of Sandstone; the Sandstones (4) contain, in places, beds of Marl, or seams of Conglomerate; the Conglomerates and Pebble-beds (3) contain seams of Sandstone; the Marls (2) sometimes contain sandy sediments, but these are more usually developed at the base; the Breccias and Sandstones (1) dovetail one into the other, more particularly in the higher portion of the division, where they are often capable of being distinguished in mapping, while in the lower portion the breccia is associated with conglomerate: the sandstone often contains beds of breccia, and marly or clayey seams appear in places in the breccia.
In the following section the beds consist of red, brown, and yellow sandstone, with pebbly seams; false-bedding is very conspicuous. They belong to the Upper Sandstone division.
The Upper Marls appear on the southern edge or escarpment of the Polden Hills, and are visible in several outlying hills in the bordering moors.
From Bridgewater the Marls extend north-west towards Watchet, and southwards through the vale of Taunton, where their boundary with the Upper Sandstone of Halse and Fitzhead is very ill-defined. In an easterly direction the Marl is overlaid by the Greensand of Blackdown, and the extension of the beds is almost concealed east of Kentisbere, where they are not so calcareous as in other places. Near Broadhembury and Kentisbere, alternations of sandstone and mottled clay, which dovetail together, are seen in the lane cuttings. The upper beds, consisting of red and variegated marls, pass upwards into the Rhætic beds at Axmouth. They are well shown at Seaton, Branscombe, and Watchet; and contain Gypsum, particularly at Watchet, and near Somerton.
Pseudomorphous crystals of Rock-salt have been noticed. in the lower portions of these beds near Sidmouth.
The underlying Upper Sandstones are generally composed of red rock, often false-bedded and in places mottled with