DIGGING, MINING AND MARKETING FIRE-CLAYS.
The extraction of the clays, feldspar, kaolins, fire-sand and other materials occurring in the plastic clay belt of the State of New Jersey, is mostly accomplished by digging pits in the beds worked, the overlying strata having been previously removed. The removal of the superficial beds, or "bearing," as it is fre quently termed, and the digging, vary somewhat in the details according to the nature of the circumstances of location, rela tion to water, cost of labor, prices of materials, transportation, and business management.
The first work on opening a clay bank, after satisfactory ex ploration, is to remove the top dirt or bearing. This is done in wagons in case it has to be carried to some distance, or else by cars on a movable track. Wheelbarrows are occasionally used. At older banks, where a large amount of clay is dug, a car-track, or tramway, generally runs from the bank to the point of delivery—main lines of railroads, or to docks on navi gable water—and in these the track is generally laid quite to the heading or face of the bank, or alongside of it, so that the cars can be easily loaded. This material is taken outside to the dumping ground. Teams are in use as the motive power, be ing cheaper than steam, and quite as effective in short distances. If any of the materials of this bearing are of probable value, they are sorted and put by themselves preparatory to future use, or are at once shipped, as desired. Whenever, in working banks, pits, or excavations, areas have to be filled, the top dirt is used for that purpose.
According to the general practice, the digging advances by a succession of contiguous pits, and the dirt of the pit which is being uncovered is thrown at once into that which has just been dug. In some cases it is sufficient to use the dirt from the top of the new pit, and the necessity of removal to dump or waste heaps is avoided. But this is exceptional, as in most localities the amount of top dirt is in excess of that needed for filling, and the surplus must be removed.
The cost of removing the top dirt depends on so many and such constantly varying conditions that it is not possible to give prices. The nature of the strata, the distance of removal, the price of labor and other items, enter into the cost.
Since the top dirt nearly everywhere is earthy, the employ ment of steam excavators or similar machinery is certainly practicable. The introduction of larger capital and more com prehensive management in the mining of these clays, etc., will be accompanied by more machinery to replace much of the slow and primitive methods now in use.
An important question is the location of the heaps of top dirt or dumpings. This is especially important at a new local ity, and care is always necessary to avoid placing the dirt on sites which are to be worked at some future time. By boring or digging small trial pits, it is easy to select areas which are not profitable for mining. Wherever the area worked over is large, they become the proper place for storing them, if the distance is not too great.
The mining of clay is generally done by digging small pits ; these are of different sizes according to circumstances of place and men to be employed. A common size is a rod square, or an oblong pit of about the same area. These are dug through the beds of value, or as deep as practicable. Generally they are made of sufficient depth to extract all of a given bed of clay, feldspar, kaolin, or other material, which may be worked, and the digging or pitting stops at the bottom of that bed. Thus in the fire-clay banks, they are dug through that stratum, although in some places where there are valuable beds under neath this, the digging is continued into these lower beds. The work is often stopped on account of the water in some pits ; the danger of caving in, water flooding and other such circum stances, determine the depths of the workings.