under the chemical action of water is favored by a warm, moist
climate and abundant vegetation. Frost and heat and cold can only
act within the few feet from the surface to which the necessary
temperature changes are limited, while water penetrates and alters
the rocks to great depths.

The pupil may explain.

In what ways the presence of joints and bedding planes assists in
the breaking up and decay of rocks under the action of the
weather.

Why it is a good rule of stone masons never to lay stones on edge,
but always on their natural bedding planes.

Why stones fresh from the quarry sometimes go to pieces in early
winter, when stones which have been quarried for some months
remain uninjured.

Why quarrymen in the northern states often keep their quarry
floors flooded during winter.

Why laminated limestone should not be used for curbstone.

Why rocks composed of layers differing in fineness of grain and in
ratios of expansion do not make good building stone.

Fine-grained rocks with pores so small that capillary attraction
keeps the water which they contain from readily draining away are
more apt to hold their pores ten elevenths full of water than are