Fire Clay

Fire Clay

With the rapid development of Canadian industries calling for the use of fire-brick for the lining of furnaces or cement-kilns, for constructing brick-kilns or coke-ovens, for lead-furnaces, etc., the question has often arisen whether the provinces within the Dominion have not the necessary raw materials for the manufacture of such refractory wares.

The materials came in part from Great Britain, and part from the United States. Those supplied by the latter country are obtained largely from Pennsylvania and Ohio, and when shipped to distant points, such as British Columbia, the item of transportation is a serious factor.

Scotch fire-brick is used both in eastern and western Canada, but in the latter case the shipments are made by water route to Vancouver.

During the past four years I have been investigating the clay-deposits of Canada, for the Canadian Geological Survey, and while all types of clay have been included in the study, special pains have been taken to ascertain the occurrence of refractory clays. As a result of this work we are able to report on the existence of beds of refractory clays at the following localities: Inverness and Shubenacadie, Nova Scotia; St. Remi, d’Amherst, Quebec; Dirt Hills and Cypress Hills, Saskatchewan; Sumas Mountain, near Clayburn, B. C., and Kyuquot, on northwestern Vancouver Island. A map of Canada, showing the fire-clay deposits, is given in Fig. 1.

It is possible that other deposits may be discovered in the future in districts remotely located from the present lines of railroad.

map of canada

Of the occurrences mentioned only those of Sumas mountain and Kyuquot are at present utilized. The vast deposits of the Dirt Hills are still attractive for development.

The St. Remi deposit is not discussed in this paper, since it is of more value for making paper than for fire-brick.

A fact which enhances the value of some of these deposits is that they are adapted not alone to the manufacture of fire-brick, but can in some cases also be worked for use, wholly or in part, in the production of stoneware, terra cotta and sewer-pipe.

Nova Scotia

A most remarkable clay-deposit of undetermined age is found in the Musquodoboit valley, and near Shubenacadie, both areas being a short distance north of Halifax, the latter along the line of the Intercolonial railway. The material is a highly-plastic clay, of dark gray, white, or mottled red and white color, lying beneath the glacial drift, and resting probably on bed-rock. Scattered lumps of lignite were found in the clays of both localities, and it was hoped that thin sections of it might aid in determining the age of these beds, but the material is not sufficiently well preserved to be of value in this respect. It seems probable, however, that these clays may be of the same age as the Cretaceous fire-clays of New Jersey, since they bear a remarkably strong resemblance to them.

It is very difficult to outline the exact area underlain by this deposit, owing to the mantle of glacial drift overlying the region, but the fact that the material is found at several points, extending over a distance of several miles, indicates its possible extent. A number of borings were made at those points where the drift cover was thin.

Musquodoboit Valley.—The broad valley of the Musquodoboit river is bordered by rather high, even ridges with gentle slopes, while the valley is floored with glacial drift, which overlies un-consolidated sediments of unknown depth, and referred to as underclay. This underclay outcrops at a few points along the banks of the river at the village of Middle Musquodoboit, and for several miles above, also on Murphy brook and Paint brook, two small streams entering from the north.

The underelay has attracted attention for many years by reason of its bright color and high plasticity. But at most points it is covered by a stiff boulder clay, in which lumps and patches of the underclay are often included.

A limited number of borings made revealed the fact that the deposit is not one solid mass of high-grade clay, but that it is a stratified formation made up of fine white clay, colored clay, and sands, with occasional layers of lignite, and some scattered pyrite concretions. In other words it closely resembles many of the New Jersey Cretaceous clay-occurrences. Many of the colored portions bleach strongly on exposure to the weather.

A number of borings, made at different points, indicated thicknesses of at least from 25 to 50 feet.

The plasticity of the clay is usually good, even the silty beds possessing fair plasticity—in fact, enough to permit their being molded.

Along the flood plain of the river there are some large patches of very stiff and very adhesive clay of light gray or bluish color, which the local residents regard as fire-clay, but it is not.

The deposit in this valley is undoubtedly extensive, but before developing it a number of additional borings should be made, as in the Geological Survey work it was not possible to spend the time and money on it that a private corporation could.

The physical tests given in Table I. represent the properties of, Sample I., a red and gray mottled clay from Murphy’s brook, and Sample II., a light gray clay from farther up the same brook.

physical tests of clays

Sample I. burned steel hard at Cone 03; its form was still preserved at Cone 9, but the fire-shrinkage was somewhat high. It is not a good fire-clay.

Sample II., which can be regarded as a fire-clay, did not become steel hard until Cone 1, due to its more refractory character. In its natural condition it burns rather dense for a fire-brick, but the body could be opened up by the addition of ground-up brick.

The chemical analyses of the clays are given in Table II.


I. Gray clay, the physical tests of which are given in Table I., column II. M. F. Connor, Dept. Mines, analyst.
II. Average sample of white clay from 18-ft. bore-hole.
III. Average sample of mottled clay from 15-ft. bore-hole.
IV. Floated mottled clay.
V. Floated white clay.

Analyses II. to V., by F. H. Mason, Nova Scotia Mining Institute, 1901.

Shubenacadie.—A light gray plastic clay is exposed along the Intercolonial railway tracks about 0.75 mile south of Shubenacadie station. Small quantities were mined a few years ago, and shipped to a pottery near Enfield on the same line. More recently an effort was made to place the clay on the market, and a shaft was sunk by E. Thompson on his property near the original exposure. This shaft is about 30 ft. deep, and penetrates marine- and boulder-clay for 20 ft., and gray clay for 10 ft. About 7 ft. of the latter is exposed in the face of three short drifts leading from the shaft, and a boring made in the bottom of the latter showed an additional depth of 16 ft. of silty gray clay.

Borings made around Shubenacadie have shown the presence of the clay at a number of points, but sometimes the overburden is considerable, so that the winning of the clay would have to be done in part by underground methods.

Table III. gives, I., the tests of the light clay from the shaft at Shubenacadie, and II., tests of a carload-lot taken from the shaft, and shipped to the brick-works at Westville, near New Glasgow.


Sample I. is nearly steel Hard at Cone 03. It is a fire-clay, but could be also used in the manufacture of pressed brick and terra cotta.

Sample II. gives a good hard body at Cone 03. The fire-shrinkage is low, but the clay is somewhat dense burning, and would have to be opened up with grog.

An analysis of the clay made by M. F. Connor, of the Department of Mines, Ottawa, gave :


Inverness.—There are so many coal-bearing areas in which fire-clays are found under coal, that it has become a widespread custom among coal-miners to call every underclay a fire-clay. Nova Scotia is no exception to this rule; but, although there are several coal-areas within the province, there is only one known occurrence of refractory clay, and this is at Inverness.

There, overlying the Hussey seam, is a bed of clean-looking, plastic, gray clay which varies from 18 in. to 3 ft. in thickness. The clay is free from coarse sand, but occasional nodules of pyrite are found. There is not a little fine sand, however, for only 58.4 per cent of the clay passed through a 200-mesh sieve. The clay worked up with 30.8 per cent, of water, had an air-shrinkage of 8.5 per cent., and an average tensile strength when air-dried of 206 lb. per sq. inch.

Burning-tests on this clay gave :


This clay can be classed as one of moderate refractoriness. In its natural form it is to be properly classed as a stoneware clay, but if “ grogged ” it can be used for the lower grades of fire-brick. If worked, it would have to be done in conjunction with the mining of the underlying 13-ft. seam.

An analysis, made by M. F. Connor, of the Department of Mines, Ottawa, gave:



The fire-clays of Saskatchewan province all occur, so far as is known, in the Laramie formation, which underlies a large triangular area in southern Saskatchewan. The base of this triangle forms the southern boundary of the province, as far



west as the Wood Mountain district, which is included in it. From the apex of the triangle a narrow belt extends NW. to a little beyond the main line of the Canadian Pacific railway, west of Moosejaw. This area, it will be seen by reference to a map, includes the Souris coal-field and the Dirt hills.

Detached areas are found west of this, where the Laramie formation occupies the summits of some of the plateaus, and portions of elevations such as the Cypress hills.

The Souris coal-field contains no fire-clays so far as could be ascertained. The Cypress hills has white-clay deposits, probably of refractory character, but they lie too far from the railway lines to be available.

The Dirt hills area has extensive deposits of refractory character.

Dirt Hills.—These hills form an isolated elevation rising from the plains about 30 miles south of Moosejaw. A smaller group lying on their northwestern side is known as the Cactus hills. Two lines of railroad passing close to them are almost completed. One of these, the Canadian Northern, is on the east, and the other, the Moosejaw-Lethbridge branch of the Canadian Pacific, is on the NW. boundary.

While the clay-deposits in the hills are undoubtedly of considerable extent, the best natural exposures are found on the north side of the mass, where landslide masses afford excellent exposures. This is in section 28, township 12, range 24, west of the 2d Meridian.

The general topography of these landslide masses is well shown in Figs. 2 and 3, which might lead one to infer that the clays are all white, but while these predominate, other types are not wanting. The series includes white and grayish-white sandy clays, bluish and purplish clays, brown siliceous clay shales, and gypsiferous shales.

The following condensed statement will serve to show the character of the clays in this locality.

At the eastern edge of the group of knolls is a series of alternating red and brown siliceous shales, which have been referred to by some as sewer-pipe clays, but which alone cannot be used for that purpose. The individual beds of this series differ somewhat in their sandiness, and if used the entire series should be mixed together. A few scattered sandstone layers are present, but these are soft and could be easily crushed up.

Overlying these siliceous clays, and separating them from the next knoll on the west is a series of soft sandstone beds containing large scattered concretions. These are valueless.

Above these stratigraphically, but lying at the base of the second knoll going westward, are heavy beds of gray and grayish-white sandy clay (No. III.), and brownish-gray clay (No. II.), the two being separated by a thin layer of lignite. The brownish-gray clay forms a bed about 20 ft. thick in the lower part of, the knoll.

The grayish-white clay (No. III.) contains lenses of smooth white clay (No. IV.). In most cases it would not pay to separate this white clay in mining, unless the lenses are larger.

Table IV. presents tests of these four types of clays.

physical tests of clays-from-dirt-hills

Sample I. cracks badly, unless preheated at 500° C., and the tests were made on the preheated clay. It has too high a fire-shrinkage, but works all right if mixed with some of the other clays in the section.

Sample II. has to be dried slowly to avoid cracking, and is not a good fire-clay.

Sample III. stands rapid drying, and is a good fire-clay.

Sample IV. is likewise refractory, but shows higher shrinkage, and denser burning qualities, due to removal of fine sand by washing.

The white clays are also found to the southward in Sec. 24, township 12, range 24, west of the 2d Meridian, where some lignite-mining has been done, but the clay is not so well exposed, and the actual thickness is not known; but the tests of it are interesting as showing the persistence of the refractory beds. They need not be detailed here; suffice it to say that the clay has a fusion-point equal to that of Cone 31. If this white clay is washed, it yields a product free from grit, and which closely resembles the ball-clay used in the manufacture of white-ware.

For purposes of further comparison Table V. gives the composition of clays from several localities. The clay from Dickinson belongs to the same formation as the Dirt Hills clay:


Note.—I, washed Dirt Hill clay ; II, Salina, Pa.; III, Woodbridge, N. J., and IV, Dickinson, N. D.

Associated with the fire-clays at Dirt hills is also a stoneware clay which fuses at Cone 23. But of more interest is the fact that a mixture of the fire-clay, the stoneware clay and a third clay from this locality makes an excellent sewer-pipe body which takes a good salt-glaze.

Other Localities.—White clays are reported by D. B. Dowling, of the Canadian Geological Survey, from Wood mountain, and others have been noted by R. G. McConnell, as occurring in quantity on the Frenchman river in southwestern Saskatchewan.

A sample collected from the summit of the Cypress hills a few miles south of Belanger P. O. had a fusion-point of Cone 27.

British Columbia

Sumas Mountain.—One of the most interesting series of clay-deposits is that lying in Sumas mountain, east of Clayburn, on the Seattle branch of the Canadian Pacific railroad. These deposits consist of a series of shales, sandstones and a few conglomerates, and coaly beds, the whole series having a gentle southwesterly dip.

Near the base of the series there are three beds of distinctly refractory character, the section involving:


The flint-clay, as tested from a sample taken in the mine of the Clayburn Clay Co., is a feebly plastic material, with an air-shrinkage of 3.5 per cent., and when fired at Cone 9 having a fire-shrinkage of 5.7 per cent., and an absorption of 7.1 per cent. It fused at Cone 33.

The lower fire-clay is a hard, dark gray material, which worked up with 15 per cent, of water to a mass of moderate plasticity having an air-shrinkage of 3 per cent., and an average tensile strength of 65 lb. per sq. inch.

Firing-tests gave :


This clay shows low fire-shrinkage, moderate absorption, and burns to a good fire-brick body. Other samples tested showed a fusing-point of Cone 32. A sample tested from the deposits of the Kilgard Co. on the other side of the mountain gave similar results. The product competes successfully with Scotch and Pennsylvania brick.

The so-called china-clay, which underlies the lower fire-clay, is a fine-grained, whitish shale, sometimes smooth and soft, at other times hard with a conchoidal fracture. Throughout this clay are scattered numerous small limonite spots. It is not a fire-clay as it fuses at Cone 22-25, according to samples tested. Careful grinding and washing gave about 18 per cent, of washed product, which was quite plastic, and worked up into a smooth, but not perfectly white-burning body. It cannot be used for china, but could be employed as an ingredient of a cheaper pottery or wall-tile body if necessary.

Kyuquot, Vancouver Island.—On the western side of Vancouver Island, near its northern end, there is a deposit of residual clay derived partly from a metamorphosed volcanic rock, presumably a rhyolite. The product as shipped consists of a mixture of clay and lumps of the partly-decomposed rock, and is of distinctly refractory character, since its fusion-point is Cone 30. Its occurrence is interesting, because few residual fire-clays are worked in North America, and because of its occurrence in a glaciated region. Moreover, it is sufficiently extensive to be of commercial value.


From what has been said above it will be seen that there are several possible sources of supply of refractory clays, some of which are sufficiently extensive to support a healthy industry. With the rapid industrial development of Canada, there is an increasing demand for refractory bricks of all sorts, and it is safe to predict that many of the deposits now lying idle will be put to a good use in the near future.

fire clay