With these the building rests upon a number of hollow cylinders, or wells, of brickwork or masonry, which form supports in the same way as hollow piles or tubular foundations.

The masonry is first built to a height of about 4 feet upon a wooden curb or frame of the size of the work; this is then undermined and allowed to sink its full depth into the ground; another 3 or 4 feet is then added, the structure is again undermined, and so on until the required depth has been attained.

The masonry must be of first-rate quality, and the undermining must be equal all round, or the work will be strained and crack.

Well foundations are extensively used for ordinary buildings in India; but in this country they have been restricted to cases in which a support is required for heavy wharf walls and other structures.

Pile Engines of various kinds are used for driving piles into the ground.

In all of them a heavy block of iron or wood called a " ram" or "monkey" is raised by a rope or chain over a pulley to the top of an upright frame and then allowed to fall suddenly upon the head of the pile, being guided in its descent by arrangements which vary considerably in different engines.

There is some difference of opinion as to whether piles are best driven by blows slowly delivered by a heavy monkey falling through a considerable height, or by a light monkey, with a short fall, delivering blows in quick succession. The latter plan is, however, in nearly every case by far the best, as the heavy blows crush the foot of the pile just above the shoe, convert it into a large mass or ball of fibres, which prevents it from penetrating further.