It is customary to have on the ground at the side of the pit a platform of a few boards, on which the clay or other material is thrown, and if needed, the clay is sorted into different grades. This sorting is done piece by piece as the spits are dug. A gouge spade is used in digging the clay. This differs from the common spade in having its blade cylindrical, and the upper edge is broader than that of the common spade, a tread to re ceive the weight of the pitman, neceesary to cut down into the solid clay bed. The lump of clay, or spit, as it is called, thus loosened is taken by another workman, who cuts out any nod ules of pyrites that may be in it, or any other foreign matter which can be removed by a knife, and thrown on the platform. This workman sorts the clays for ware, fire-brick, paper, alum, pipe, or other grades. The pitman confines his operations to cutting down the clay, continuing this over the pit area, and then begins a new spit level, and so proceeds till the bottom of the bed is reached.
In some of the clay banks the working floor or base is lower than the top of the clay bed, or on a level with the bottom of the bank. The digging of these banks is not properly by pits, although it goes forward by a succession of pit-like excavations. The platform fo,r the clay is below ; the carts are driven to the side of the bank and loaded at once by the workmen ; or the clay is carted to heaps near by and there stored, each grade or variety by itself, or it is taken to boats or cars for transporta tion to market.
Wherever the sides or the walls of the pits or banks are liable to fall in, these have to be strengthened and the workmen pro tected by planking and bracing. In pits of ordinary size, three heavy planks on a side are sufficient, with bracing timbers placed across between the opposite sides. Excavation into the bank and above a working level is not often attended by such dangers. The lateral thrust in pits appears to be the more common cause of slides or caving. In sinking pits it is neces sary and customary to leave walls of clay r to 2 feet thick on the sides which have been worked. These act to hold up the ground and keep out the water. Most of the danger from slides comes from these walls, and the pressure of wet drip behind them. After the pit is dug and before it is filled up, a part of the clay walls is taken out so that as little as possible is left in the ground.
Occasionally picks are used instead of the gouging spade, when the clay is very hard and compact. At a very few local ities blasting by powder is employed to break up extra hard clay or strong layers associated with it. Undermining and splitting off large masses of earth, clay, etc., by wedges or powder are practiced at banks where the materials are of a coarser or less valuable character. This is common at the red
brick clay banks. It consists in digging under at the foot of the bank as far as can be done with safety, and then either allowing the undermined mass to tumble of itself, or to force it off by using powder or wedges at the top of the bank. In this manner hundreds and thousands of tons are tumbled down at once and broken, making the handling much easier than the removal of an equal weight by spading and shoveling down from the bank.
As the beds of clay are nearly always impervious to the flow of water, there is no water to be removed, except the very little rain-water which falls or the leakage from the surface drain about the top of the pits. This is usually allowed to accumu late in a deeper corner of the pit, and is bailed out from time to time with a bucket. As the time for sinking a pit of the ordinary size does not often exceed two or three days, there is little water from these sources. The greatest amount of water comes from the sand or other layers which are sometimes in terstratified with the clay, and which allow the water to perco late quite freely through them. Sometimes the clay bed is found to be quite sandy in the middle and to allow water to leak through.
At most of the clay banks the bed of clay is underlaid by sand, kaolin, or sandy clay, and these strata are generally full of water, so that the bottom of the pits is wet, and the pits soon fill with water if it is not pumped out or they are not filled at once with earth. In banks where all the clay bed is above the working floor, open ditches or partially covered drains are conl structed so that the water can run off without further inconveni ence or cost.
In pits the water has to be hoisted to the level of the work ing floor, and thence carried off by drains. Various modes of raising water are in use ; the most common is by a pump worked by hand at intervals, as it is necessary to keep the pit clear and in working condition.
Hoisting by buckets and a windlass has been used in a few localities. Steam power has also been employed in some places, where the depth of the pits and the surrounding wet ground, as in tide-meadows, furnished a large quantity of water to be raised. The judicious arrangement of the loCa:tion and appli ances so as to avoid heavy expenses in keeping water from the pits, has much to do with the profits of clay digging. Com prehensive plans and skillful management are as important in this as in any other department of industry. The profits of clay digging have in some instances been very large, but for lack of judicious plans they have not been long continued.