Solid rock under the whole, of the building affords a first-rate foundation if it is perfectly uniform in character, thick enough to bear the weight safely, with an upper bed approximately horizontal or perpendicular to the pressure upon it, and not liable to be affected by atmospheric influences.

In such a case it will be necessary only to break down projecting points, cut away loose and rotten parts, making good and carefully filling in all cavities with concrete.

If the strata are inclined there is danger of the upper layers sliding over the lower, and also expense in " benching " or levelling in steps.

Again, if the rock is (like some clay slates, for example) of a nature to disintegrate when exposed to the weather, it should be protected by a bed of concrete.

The foundation should be so arranged that the pressure upon the rock does not exceed one-eighth of that necessary to crush it.