284

BOOK VIII.

A— Mortar. B —Upright posts. C— Cross-beams. D— Stamps. E —Their heads.F— Axle (cam-shaft). G —Tooth of the stamp (tappet). H —Teeth of axle (cams).

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can remove with a shovel the fine sand, and likewise the coarse sand andbroken rock, into which the rocks have been crushed ; this board can belowered, so that the mouth thus being closed, the fresh rock thrown in maybe crushed with the iron-shod stamps. If an oak block is not available,two timbers are placed on the ground and joined together with iron clamps,each of the timbers being six feet long, a foot wide, and a foot and a half thick.Such depth as should be allowed to the mortar, is obtained by cutting out thefirst beam to a width of three-quarters of a foot and to a length of two and athird and one twenty-fourth of a foot. In the bottom of the part thus dugout, there should be laid a very hard rock, a foot thick and three-quarters of afoot wide ; about it, if any space remains, earth or sand should be filled inand pounded. On the front, this bed rock is covered with a plank ; thisrock when it has been broken, should be taken away and replaced byanother. A smaller mortar having room for only three stamps may also bemade in the same manner.

The stamp-stems are made of small square timbers nine feet long andhalf a foot wide each way. The iron head of each is made in the following