them remain in this mill until they are ground to the state of sand and mud. Now and then one of the fragments is tossed up beyond the reach of the waves, and is contributed to the wall of the beach. In very heavy storms these pebbles which are thrown inland may amount in weight to many tons for each mile of shore. The study of a pebbly beach, drawn from crest to the deep water outside, will give an idea as to the history of its work. On either horn of the crescent by which the pebbles are imported into the pocket we find the largest fragments. If the shore of the bay be long, the innermost part of the recess may show even only very small pebbles, or perhaps only fine sand, the coarser material having been worn out in the journey. On the bottom of the bay, near low tide, we begin to find some sand produced by the grinding action. Yet farther out, below high-tide mark, there is commonly a layer of mud which represents the finer products of the mill. Boulder beaches are so quick in answering to every slight change in the conditions which affect them that they seem almost alive. If by any chance the supply of detritus is increased, they fill in between the horns, diminish the incurve of the bay, and so cause its beach to be more exposed to heavy waves. If, on the other hand, the supply of grist to the mill is diminished, the beach becomes more deeply incurved, and the wave action is proportionately reduced. We may say, in general, that the curve of these beaches represents a balance between the consumption and supply of the pebbles which they grind up. The supply of pebbles brought along the shore by the waves is in many cases greatly added to by a curious action of seaweeds. If the bottom of the water off the coast is covered by these fragments, as is the case along many coast lines within the old glaciated districts, the spores of algae are prone to take root upon them. Fastening themselves in those positions, and growing upward, the seaweeds may attain considerable size. Being provided with floats, the plant exercises a certain lifting power on the stone, and finally the tugging action of the waves on the fronds may detach the fragments from the bottom, making them free to journey toward the shore. Observing from near at hand the straight wall of the wave in times of heavy storm, the present writer has seen in one view as many as a dozen of these plant-borne stones, sometimes six inches in diameter, hanging in the walls of water as it was about to topple over. As soon as they strike the wave-beaten part of the shore these stones are apt to become separated from the plants, though we can often notice the remains or prints of the attachments adhering to the surface of the rock. Where the pebbles off the shore are plenty, a rocky beach may be produced by this process of importation through the agency of seaweeds without any supply being brought by the waves along the coast line.