When first invited to read a paper on this subject, it appeared to the writers that there could scarcely be anything in it, to interest an audience of mining-engineers. It is, however, perfectly true that what we are accustomed to see frequently becomes utterly commonplace to our own vision, and yet it may be interesting and even instructive to those differently placed.

Of the three methods in common use for supporting mining-excavations, viz. : — (1) Masonry, (2) iron or steel, and (3) timber, the latter is the only kind adopted in the iron ore-mines of Cumberland and Furness, and the annual bill for mining-timber is a serious item at practically all the mines in that portion of the mines-inspection district.

Larch and Swedish or Norwegian pine are the varieties of timber most generally used, but American pitchpine is often used for shaft-timbering.

The different methods of timbering naturally vary according to the character of the deposit to be mined. We have therefore a variety of modifications in working the following kinds of deposits, viz. : — In Furness — (a) Dish-like deposits, and (b) vein-like deposits. In Cumberland — ( c) Partially stratified or bed-like deposits, (d) irregularly-shaped deposits, (e) vein-like deposits, and (f) dish-like deposits.

It is no part of our present purpose to describe the interesting geological features of these haematite-deposits. This subject will be found treated very exhaustively by Mr. J. D. Kendall in The Iron-ores of Great Britain and Ireland¹ and also by Dr. C. Le Neve Foster in his comprehensive Text-book of Ore and Stone Mining.²

We have, however, thought it advisable to introduce a typical section (Fig. 1, Plate X.), illustrative of an important deposit, with the view of affording a better grasp of the subject treated of in this paper.

A complete description of mine-timbering should naturally begin with the shaft but, inasmuch as the systems of shaft-timbering in general use exhibit no distinctive features, it is not proposed to enter in detail into this part of the subject. One or two circular shafts are to be found amongst very old mines, but all shafts sunk of recent years in connexion with Cumberland and Furness haematite-mines are rectangular. The ordinary sizes are from 10 to 12 feet long by 4 to 5 feet wide, but the newer shafts are larger.

In Furness, the system adopted for securing shafts is the common method of sets or frames ; Figs. 2, 3 and 4 (Plate X.), showing the plan and section of a winze or staple-pit. The sets consist of four pieces of squared timber, A (Fig. 2), which are fixed in the shaft about 3 feet apart ; and boards, 1 inch thick, termed "wadding-spiles," a (Figs. 3 and 4), are placed behind the set to keep back the loose ground.

In Cumberland, the method in general use is even more elementary. The sets or frames consist of planks, from 3 to 6 inches thick, placed close together on their edges. Each set is carefully wedged to the. solid ground, and pieces of 5 or 6 inches square pitchpine, cut diagonally across, are nailed in each corner, thereby tieing all the sets firmly together.

Figs. 5, 6 and 7 (Plate X.) illustrate the method of supporting the main levels of the Furness district. Two uprights or forks, A A (Figs. 6 and 7), support a bar or head, B, placed horizontally, and these form a course of timber. The forks are faced and collared, i.e., hollowed out. e, to allow the head to receive a full hearing-surface. To guard against side pressure, a nog, 0, is driven into the head, close to the face of the fork.

In Cumberland, the nog is a spike-nail, but in Furness a wooden plug' is used, an auger-hole being previously bored in the head to receive it.

When the side pressure is great, a plank is wedged between the forks, close up to the head, for additional security.

The head is covered by spiles, D, D, formed of deal boards, cut into regular sizes, 4 feet long, 6 inches broad, and 1 inch thick. In very heavy ground, larch spiles, 6 to 8 feet long by 3 inches thick, are used.

In soft or gravelly ore, the spiles, H, are driven over the last head up to the face of working, Fig. 9 (Plate X.). As the working proceeds, the spiles are driven further, until there is room for the insertion of another head. In relatively hard ore, the spiles are placed flat on the heads as shown at D, Fig. 9.

According to the Special Rules in force in the Furness district —

No work-person when working soft or gravelly ore shall allow the fore-breast to be more than 4 feet in advance of the timber props, nor when working ore which requires blasting, more than 6 feet in advance of the timber props.

Boards or spiles, C, are also placed behind the forks in tender ore, in the same way and for the same purpose as they are placed over the heads (Figs. 6 and 7, Plate X.).

Fig. 7 also illustrates the method adopted in turning-off a side working. An uptaker or cross-head, B, is put under the ends of the heads at the side from which it is intended to turn off the new place.. The uptaking set usually embraces four heads, the forks of the two central heads being removed after the uptaker or cross set, A B A, is firmly fixed in position. The cross-section (Fig. 6) shows an end view of the uptaker and the timbering of the cross-drift.

The drifts are usually driven to allow of the use of 9 feet heads and 7 feet forks.

In dealing with veins or ginnels a different system of timbering is necessarily adopted.

In Lancashire, the ore in these ginnels is generally cut off by a hard limestone-roof, and as this roof does not readily collapse or crush, it not infrequently happens that height after height of the ore is taken away without the roof following. In cases of this description, we have therefore (except for the timber which is put in) huge empty chambers, which are among the most difficult of mining problems to work safely and satisfactorily.

When the veins are narrow, stays are inserted from side to side like headtrees, those nearest the top being covered with boards and chocked up to the roof. These serve the purpose of steadying the sides or cheeks of the vein and keeping the roof secure.

In wider veins wooden pillars are built, in what Dr. Foster terms the "pigstye" system of timbering, ³ i.e., logs laid crosswise, one above the other.

In working the softer ores of Furness, similar pillars are frequently built, the wood recovered from old workings being utilized for this purpose. In these cases the logs are generally laid close together, so as to form solid wooden pillars, which are intended to keep open special airways or travelling roads. Only a small proportion of sound timber is recovered, but much that would otherwise be useless is serviceable for the erection of these pillars.

Passing along the drift, the timbering of which has been described, we arrive at one of the vertical rises, Figs. 8, 9, 10, 11, 12 and 13 (Plate X.). These rises are a special feature of the Furness mines, and with one important exception are not adopted in the same systematic way in Cumberland. The exception is Hodbarrow, where a dish-like deposit similar to those of Furness is largely worked according to Furness methods. The rise is practically a shaft, but instead of being sunk it is excavated from the bottom upwards and carefully timbered.

The rises are usually made 6 feet by 4 feet, with two compartments, as shown in Fig. 11. One division is used as a travelling-road, in which ladders, K, are placed at convenient angles, and stages or platforms, L, are placed at regular intervals. This division is also used for bringing up timber, a small hand-winch being usually fixed at the top.

Norway timber, or 6 inches square, is used in rises. The blocks, are placed directly over each other, united at the corners with the joint shown in Fig. 12 (Plate X.). A space of 3 inches is left between the Norway blocks by inserting a small chock, J (Fig. 10, Plate X.). The space thus left makes it easy to insert stage-planks whenever it is necessary to execute any repairs inside the rise.

The steel rails, M, Figs. 9, 10 and 11 (Plate X.) are locally known as breakers. Their object, as implied by their name, is to break the fall of the iron-ore in its descent to the bottom of the hurry, the latter being the name by which the second division of the rise, i.e., the ore-receptacle, is known. A larch pole, N, is generally used in conjunction with the steel rail, M, (Figs. 10 and 11, Plate X.).

In the inclined hurries of Cumberland, a similar object, that of breaking the fall of the ore, is attained by the use of heavy iron swinging-doors.

The rise is taken to the top of the ore, and a first or breaking-out course of timber is inserted (Figs. 8 and 10, Plate X.). It is usual to break out at the end, in preference to the side, of the rise, as the width is less (4½ feet as compared with 6 feet) ; there is consequently a smaller quantity of material to remove, and less risk of dislocation of the ground, in a somewhat critical situation. A longitudinal section of the breaking-out course, and continuation of the drift is shown at, I I, in Fig. 10 (Plate X.).

Fig. 13 (Plate X.) is a plan of the bottom of the hurry, and a longitudinal section of the same is shown in Fig. 9 (Plate X.). These figures show an arrangement of planks whereby the exit of the hurry is narrowed, so that the iron-ore may be conveyed into the small waggons used underground, and locally known as bogies, G. A door or stopper at, E, enables the waggoner to liberate the quantity of iron-ore required to fill each bogie. It will be noted that as the bottom of the hurry is required to support considerable weight in the shape of loose iron-ore, additional sets of timber, F, are placed beneath it.

In Cumberland, we have partially stratified or bed-like deposits — irregular masses and true veins, and, with the exception of the Hodbarrow mine, the system of working differs materially from that which prevails in Furness. In the first-named class, the full height of the ore is taken in the first working, whenever practicable, i.e., if its thickness does not exceed 10 or 12 feet.

When a deposit of this description is too thick to work in one height, another method is adopted, which is illustrated in Figs. 14 to 19 (Plate XI.). These drawings illustrate a typical Cleator Moor deposit of partially stratified haematite, the iron-ore being shown about 17 feet thick. In this case, workings are laid off to take a height of 9 feet in the first instance, and are driven from 15 to 20 feet wide.

In Fig. 14 (Plate XI.), two men are at work drilling holes in the solid iron-ore. It will be observed that the timber required is simply a double row of larch props, A, A. These first workings can sometimes be driven without timber, the ore being sufficiently strong to stand without other support than the pillars which are left for that purpose.

Figs. 15 and 16 (Plate XI.) show a side view or cross-section of a level which has to deal with iron-ore of a softer nature. The term softer iron-ore, it must be understood, is merely comparative, as it is necessary to blast this iron-ore, and the working is entirely in solid ground the roof is not, however, strong enough to stand supported by props alone, and full sets, B B, are inserted. In this case, the drift is driven narrower, and seldom exceeds 12 feet in width. The heads are hitched at both ends into the solid sides, C, C (Fig. 15, Plate XI.), and as the working-face gets farther away, legs are put under each end of the heads.

Large quantities of gelatine-dynamite and gelignite are used daily, and if the legs were inserted close to the face, they would frequently be blown out. This, in fact, is one of the principal difficulties to contend with when timbering ground where blasting-operations are regularly and almost continuously carried on.

Norways, D, D, i.e., Norwegian or Swedish pine, 4 or 5 inches thick, and sawn into suitable lengths, are inserted over the heads, and boards, E, E, 1 inch thick, described as coverwood, are placed over the Norways.

The space between the boards and the roof is then chocked tight with short pieces of wood. In driving the first workings, the pieces of coverwood are not usually put close together, but as shown in Fig. 16 (Plate XI.).

When the boundary has been reached, the work of taking out the pillars is commenced forthwith. The pillars on the rise side and furthest from the shaft are taken first, and removed, slice by slice, as shown at A, A, in Fig. 20 (Plate X.), by methods similar to those generally adopted in coal-mines. The striking, and almost picturesque, irregularity of the pillars may be noted in passing. These haematite-deposits are usually intermixed with masses of stone, and the first levels, in those cases, deviate considerably from a straight line. The pillars left are consequently of varying shapes and sizes.

Timber is used as previously described, props or sets being placed as may be necessary. The pillars having been extracted, the roof iron-ore followed by the limestone crushes the timbers, and becomes practically a solid mass, which is again worked through.

It will be observed in Figs. 17, 18 and 19 (Plate XI.), that the 8 feet of roof iron-ore when broken occupies 11 feet of space, and the beds of limestone immediately above the iron-ore also occupy correspondingly increased space.

The drifts in working the second time are usually driven about 9 feet square, and two methods of timbering are shown in Figs. 17 and 18 (Plate XI.). In Fig. 17, the iron-ore being of a friable nature, it is necessary to spile closely. This is done by driving split Norways or spiles, A, A, over the last headtree and up to the face, the tail-end of the spiles being caught under the previous head. The spiles are usually about 8 feet long, 6 inches wide and 3 inches thick, and as the iron-ore is extracted, the spiles are driven forward until there is room for another head.

Short pieces of planks or boards termed listing-pieces, B, B, Figs. 17, 18 and 19, are nailed to the legs, for the purpose of steadying them until they are weighted by pressure of the ground.

Figs. 14 to 19 (Plate XI.) are really a combination of sketch and section, and have been designed with the view of conveying a clearer conception of the methods of timbering employed.

Fig. 18 is a cross-section of the roadway, and Fig. 19 (Plate XI.) a longitudinal section at the working-face. Here we have exhibited another common form of spiling. In this case, the robbery consists of rough blocks of iron-ore, the original deposit having been hard haematite corresponding to Fig. 14 (Plate XI.) in the first working.

The spiles, C, C, are round larch poles, about 8 feet long and 4 to 6 inches in diameter. They are driven over the head up to the face in the same way as flat spiles, the point of the spile being usually wedged under a lump as at D, Fig. 19 (Plate XI.). Two, three or four spiles are put over each head as required, occasionally no other covering is needed ; but generally flat boards, 1 inch thick, E, E, are laid across as shown in Figs. 18 and 19 (Plate XI.).

The second working having reached the boundary, arrangements are made to recover the 2 feet of iron-ore, F, F, F, which is shown as being still left over the wood (Figs. 17, 18 and 19, Plate X1.). As a role this roof iron-ore is easily and expeditiously obtained by cutting out the centre poles between the heads, beginning with the timber nearest the boundary. If the ore be of a friable nature, and thoroughly crushed, it will readily run through the hole thus made; if it be of a harder texture, a long crow-bar, termed a proddling-bar, is used to lever down the lumps.

No attempt is made to support the limestone in this instance, beyond what is necessary to secure the safety of the workmen. To effect this object, strong spiles are driven over the headtree, after the ore has been extracted. Of course, during the last operation, considerable quantities of limestone are intermixed with the ore. As much of this stone as possible is thrown back into the abandoned workings ; but where this is not practicable, it is sent to bank.

As already stated, timber is solely used for supporting haematite-mining excavations in this district, and it may be remarked as somewhat strange that in the iron-producing mines some systematic attempt has not been made to supersede timber, at any rate to some extent, by the use of iron or steel.

Without entering into the general question of timber versus iron or steel for pit purposes, and conceding that in these mines iron or steel props or girders could not be used exclusively, there can be little doubt that, in many cases, their adoption would be of appreciable advantage.

Dry rot is a serious factor in curtailing the life of mining timber, but practically nothing is attempted to stop the ravages of this insidious and destructive enemy. In addition, the presence of very dry timber in the mine entails a continual risk of fire, and the disastrous effects of fires in and about mines have been too often witnessed to need emphasis.

The remarks and recommendations of Dr. C. Le Neve Foster in his recent report on the Snaefell disaster⁴ may very appropriately be referred to in this connexion. Dealing with the prevention of fire, he states that he "would try to arrive at the desired end by one of two methods (1) rendering timber non-flammable, i.e., not easily ignitible ; or, better, (2) replacing it by non-combustible materials such as masonry, brick-work, concrete, iron, or steel." ⁴

To achieve the first-named object, Dr. Foster recommends the Henry Aitken⁵ method of impregnating the timber with hygroscopic salts. Timber treated in this way is said to be not only difficult to ignite, but is also rendered free from the attack of dry rot ; so that two of the dangers usually regarded as inseparable from the use of timber in dry mines appear to be dealt with very satisfactorily by this process.

In conclusion, the thanks of the writers are due and are hereby tendered to the Barrow Haematite Steel Company, Limited, the Hodbarrow Mining Company, Limited, and Montreal Mines for the diagrams which they kindly prepared to illustrate the methods of timbering in use in Furness and Cumberland respectively.

1 Messrs. Crosby, Lockwood & Son, 1893.

2 Messrs. Charles Griffin & Co., 1894.

3 Text-book of Ore and Stone Mining, by Dr. C. Le Neve Foster, 1894, page 234.

4 Reports on the Circumstances attending an Underground Fire which Occurred at the Snaefell Lead-mine, 1898.

5 Patent Specification, No. 13,749, August 31st, 1889; and Trans. Inst. M.E., vol. x., page 531.

Prof. H. Louis (Newcastle-upon-Tyne) regretted that the authors had not expressed their opinion as to the method of using a forkprop and round cap employed so largely in that district. That system was invariably adopted in the Cumberland iron-mines, and be thought that it was a method which could not be too strongly condemned. It was obvious that unless the prop was hollowed out to the exact radius of the section of the cap, the prop might be split. Members who had seen Cornish and Cumberland methods of timbering could not doubt that the Cornish was the superior method. He would like to know whether any of the methods adopted in some of the large American ironstone-regions had been tried with advantage for removing a slice of 8 or 9 feet in thickness, and running in barren rock from the surface to fill up the spaces as the iron-ore was taken away. There had been many experiments in America, and it was found to be the cheapest and best method of working.

Mr. W. Spencer (Leicester) remarked that limestone sometimes formed a good roof, and if so why was part of the ore left to be taken out afterwards?

Mr. H. R. Hewitt (H.M. Inspector of Mines, Derby) thought that the method of timbering described would be insufficient in shafts of great depth, and would be glad if the authors would give the depths of the shafts and say whether the sides were strong enough to secure safety.

Mr. A. H. Stokes (H.M. Inspector of Mines, Derby) stated that similar methods of timbering were carried out in the lead-mines of Derbyshire.

Mr. J. L. Hedley (Newcastle-upon-Tyne). replying to the discussion, stated that the method of cutting the top of the prop described in the paper was advantageous on account of the weight and the subsidence of the ground above. The American system of timbering had been tried at the Hodbarrow iron-mine in Cumberland, where the deposit was about 120 feet thick, but the system had now been abandoned. At another mine in Lancashire, where there was a similar deposit, the system was not adopted, as they did not know how far the deposit extended downwards. The depth of the shafts varied, and at one mine a depth of 900 feet had been attained without reaching the bottom of the deposit. He might say that Cornish miners, who were largely employed, always adopted the Cumberland method of setting the timber.

Mr. Arthur Hassam (Maryport) wrote, that the question of timbering in mines was one of such great importance, that the thanks of the members were due to the writers for bringing the matter forward in so able and interesting a paper. There was much which the coal-miner might learn from the application of the various methods of supporting the roof and sides in ore-mines, where the enormous extent of the mineral mass, the want of stratification, and the frequent absence of cohesion, necessitated very great skill and ingenuity in fixing adequate supports. Sometime ago it was his privilege to visit, in company with Mr. Leek, several of the mines referred to, and he was much struck with the great skill of the ore-miners in dealing with, and fixing the great logs of larch and pine ; and with the clever spiling, in driving workings in gravelly ores. But, perhaps, the most striking point of interest was the method practised at Hodbarrow iron-mines, of working a dish-like deposit of haematite from the base upwards, by the building up of successive square sets of heavy pitchpine, as shown and described by the authors. The method of jointing was very ingenious, and each piece of wood was cut to template by special machinery erected on the surface. The manager stated that the method was highly successful, where the ore was hard, but that it would not answer in soft ores. The system of boring holes in the heads, and fixing nogs to support the forks or legs was simple and effective, but it seemed to have the effect of weakening the head. He suggested that a better plan would be either to nail brackets on to the head or to fix a cross stay. Very little British grown timber appeared to be used in the iron-mines except larch, and a lesson in this respect might be taken by many colliery owners and managers. Other varieties of English grown timber were used in coalmines, with very indifferent results. Most mining engineers will be of the same opinion as the authors, as to the superiority of steel girders to timber for mining supports — at all events for permanent or road-work, if not for face-work. It took up less space, was stronger and more durable, and could be used over and over again. The first cost was against its use, but its advantages and final economy and efficiency were so evident that its use was gradually but surely extending every day. He could fully endorse the writers' remarks as to the danger of fire arising from the use of timber in mines. In several instances of gob-fire in coal-mines, which had come under his notice, the seat of ignition had been timber, which had been left behind in the goaves. The original heating had doubtless been due to the chemical action of the minerals, but the dry timber had formed a very ready combustible, probably at a much lower temperature than would have been necessary to ignite the surrounding mineral, notwithstanding that the latter was the active agent. Further, apart from the danger of fire, the decomposition of timber gave rise to explosive gases, and he believed that several slight explosions of gas generated in this manner had occurred in metalliferous mines. It would be interesting to know the cost of the timber used per cubic yard of ore extracted, both in the spiling systems, where larch was the usual timber, and in the square-pine set system as adopted at the Hodbarrow mines.

The Chairman (Mr. George Lewis), in proposing a vote of thanks to the authors of the paper, said that the question of timbering seemed to give rise to differences of opinion. In various districts, certain systems of timbering had been employed for generations for reasons which were not easily explained. But he thought that the workmen knew more about their particular district and its requirements than did those who casually visited it. He was therefore loth to condemn a system of timbering about which he had had no opportunity of ascertaining its utility. It did not appear desirable to place a round piece of timber over the square end of a prop, but there might be some particular reason which would cause him to alter his opinion.

The resolution of thanks was adopted.