what striking. For the practical lessons to be derived from a study of this kind of irregularity in coal deposits, it is sufficient to know that they are the result of denudation after the formation of the coal-bed, and of subsequent filling up with the shale or other kind of rock by which the roof of the coal has been formed.

In the Memoirs of the Geological Survey-the South Staffordshire Coal-field, by J. B. Jukes, F.R.S.-it is shown that the Staffordshire thick-coal, which is about thirty feet in thickness, south of Bilston, is in reality made up of twelve or fourteen separate coalseams; and that these seams, although they are so close together in places south of Bilston and towards Dudley as to give them the appearance of one very thick coal-bed, are nevertheless, in more northerly parts of the coal-field, as at Bentley, Wyrley, Pelsall, and Essington, worked at from five to fifteen or twenty fathoms apart. Mr. Jukes very properly observes, "It may well be doubted, whether any single bed of coal is even more than two or three feet in thickness, and we may therefore take it for granted, that every bed which exceeds that thickness, over any considerable space, is in reality a compound seam, made up of two or more beds resting on each other, with or without 'partings' of shale, &c., between them."

Instances of this kind of separation in coal-beds are to be met with in the majority of coal-fields, and many examples might be given of coal-seams being sufficiently near to each other in one part of a very limited colliery district, to be worked together as one seam; whilst in other parts of the same district they are divided by several fathoms of coal-measures strata. The most remarkable phenomenon of this kind which I have been made acquainted with is shown by fig. 4.

Fig. 4.

E

D

The following particulars respecting it have been supplied by Mr. Stewart, of Bristol, who for many years followed the profession of mining engineer to the coal mining districts near Swansea. The distance from D to E is not more than 80 yards; the " partings S S consist of fine blue shale, and have a maximum thickness of 10 feet each: the three small coal seams separated from each other, are each two feet in thickness, and on each side, as at D and E, they come closely together without partings, and form a 6 feet coal bed. How far these conditions may have been maintained through a distance transversely to this section is not known, as it was to be seen in a perpendicular cliff 200 feet high, where the coal-measures throughout the distance shown by the section were laid bare.

"Swells," or "rolls," and "nips," are names given to a rising up in the floor of a coal bed, and where the roof and floor both swell out, so as to reduce the thickness of the bed. "Balk" is a name applied by the colliers of Newcastle, to the "want" illustrated by

fig. 3. "Check" is just another name for a dislocation; and “Vs' is a very convenient, and not inappropriate expression for the plane of fracture, where a displacement of the beds has taken place.

The study of faults is one fraught with interest to the geologist; but to the mining engineer, it is even more so, for, upon a due knowledge of the phenomena are depending, at this moment, the pecuniary success or ruin, or at least serious embarrassment, of many mining enterprises; and to this we may add, the reputation of the engineer, and the lives of the workmen. The Cockfield-felldyke, already noticed, may be cited as an example of many instances to be met with, of the effect of such faults on the water contained in the strata contiguous to mining works. On each side of this dyke, and between its vertical faces and the adjacent rocks, there occurs about six inches of strong clay, by which the dyke is rendered so completely impervious as to dam back the water of the country for miles in the direction of the fault. I know the case of a colliery, where a trial shaft having been sunk to a considerable depth, entailed a very serious outlay, and resulted in abandonment and heavy loss, owing to the large feeders of water met with. After the abandonment of this unsuccessful trial, another site for sinking was fixed upon but a short distance from the first shaft, but on the opposite side of a dyke; here a most successful "winning" was accomplished without (in sinkers' language) "a drop of water being met with." In deciding upon the place for "dams" in a pit, and estimating the efficiency of barriers of either coal or stone, the probable existence, and the number, direction, and character of faults, require careful attention. The amount and direction of the hade or dip of faults, and the probable accompanying branches or strings of a main slip or dyke, are also points of serious importance.

Illustrated Notes on Prominent Mines.

BY THE EDITOR.

EAST CARN BREA AND WHEAL UNY.

THE Wood-cut (figure 1) on the opposite page, shows a section of the country and workings on the run of the lodes which traverse these mines, drawn on the scale of 190 fathoms to one inch. The principal workings at East Carn Brea and Wheal Uny are shown, and also the depth of the old engine-shafts at Wheal Sparnon and East Sparnon: the latter mines not being now at work, it would be troublesome to ascertain accurately the extent to which the levels are driven, and consequently they are omitted in the section. We have already, in No. I (page 47), given a section of the workings at East Carn Brea on a larger scale: the present section is purposely drawn on a small scale in order to show the geological position of these mines, occupying a killas basin between the ranges of granite. It may also be well to remark, that the Carn Brea granite range, which in the section is shown as ending on the surface about Redruth Church, extends further east as we come south of the line of section, and consquently

flanks the East Carn Brea lodes through a great portion of the length of their sett-giving that mine a geological position similar that of its great neighbours (Carn Brea, Tincroft, Cook's Kitchen, and Dolcoath) further west.

EAST CARN BREA, is worked to a depth of 50 fathoms below the adit, the engine-shaft being sunk perpendicular to the adit, and below that on the course of the lode the levels are the adit, the 26, the 40, and the 50-all shown in the section extending from the engineshaft. The adit, which was driven by the "old men," and used to be called the "silver adit," comes up from near Messrs. Magor's brewery, to the south of Redruth, under the "west end" of that town, gaining 20 fathoms of backs at the engine-shaft. The other shafts shown in the section are:-the western shaft, about 60 fathoms west of the engine-shaft and within 30 fathoms of the western boundary, sunk perpendicular to the 40; and the new shaft, to be sunk perpendicular to the 26, down 17 fathoms below the surface, and raised up against 4 fathoms from the 26; the dotted line shows the course upon which this shaft will be sunk. It may be well to remark, that the levels driven from the western shaft under the 26, called the 30 and 40, are respectively within 3 fathoms of being as deep as the 40 and 50 from the engine-shaft.

Three lodes have already been opened on in East Carn Brea, all underlying north about 2 feet in a fathom, that is, dipping away with the granite. On the northernmost, called the engine lode, the engine-shaft has been sunk; to the south of this 11 fathoms (at the 50) is the middle lode, and 25 fathoms at the same level, the south lode. Of these, the most important is the south lode, on which a splendid run of ore-ground has been opened out, which makes East Carn Brea one of the most promising young mines in the county. In consequence of the engine-shaft being sunk on the engine lode, the south lode has hitherto had to be explored by cross-cuts, which is always a disadvantage; the western shaft, however, comes down on this lode, and the new eastern-shaft will also be sunk on it below the 26. A little to the west of this new shaft the cross-course is shown, and just to the west of this the winze sinking below the 26, which has gone down in a splendid course of ore: the shaft, on the other side of the cross-course will also go down in a beautiful course of ore.

Besides the lodes already opened on, there is in this sett another lode to the north, supposed by some to be the lode worked on in Wheal Sparnon-although others maintain that the south lode is the Sparnon lode. There has been a cross-cut driven to intersect this at the 50, but the end-in which a stone of ore has been cut-let down such quantities of water that it had to be stopped for the present. There are also other lodes to the south, in the tongue of granite which I have said extends east from Redruth church, flanking the south lodes, the chief of which are: the lode called No. 2 lode, in Uny, and the Wheal Uny tin lode, and Davies's lode. The crosscourse shown in the section, disturbs the lodes in rather a remarkable manner some of the lodes, at the same levels being heaved considerably, while others are very little disturbed. On the whole, however, the lodes are not much disturbed in their course for if one branch of a cross-course heaves them considerably, another branch is generally found throwing them back again.