Then, as a result of the transgressions of the sea, what was once a region of conglomerate may be later found far out under the sea and there is thus laid down over the conglomerate beds, strata of sandstone, slate, or limestone, depending on how far the sea advances. So we find rocks with all sorts of neighbors above and below; limestone above conglomerate, conglomerate above slate. These changes take place over vast regions and from the original uniformity in the arrangement of the rocks there necessarily results a similar uniformity in the results of this "shuffling," and no matter what changes may be made afterward by raising them up into shore cliff and mountain and by other earth movements, and by the endless reshaping by weather and wave, there still remains that underlying harmony which, with variety, gives to rocky shores their picturesque beauty. Harmony and variety are necessary in all forms of art--pictures, literature, music--and the conditions governing harmony and variety are always found hand-in-hand in the art work of the sea and its helpers. The difference in texture in different kinds of rock, for example, and in different parts of the same rock, cause them to yield in different ways and degrees to the action of wave, wind and weather; so there is sure to be great variety in the shapes they take as they are worn away. HARMONY, VARIETY, AND THE ART WORK OF THE SEA FAMILY LIKENESS IN ROCK FORMS Yet, with all their differences, the shapes rocks take--sandstone compared with granite, for example--are so characteristic that one soon learns to tell a long way off what kind of rock a distant landscape is made of. There is inevitably a certain type resemblance, since all sandstone is of the same general texture and weathers in the same way. NATURE'S BUILDING BLOCKS AND THE SEA Then take the natural division into blocks made by joints in the rocks to which cliffs like the famous Castle Head at Bar Harbor owes its striking form. These blocks are so nearly true that you feel sure they must have been cut by stone-masons, and yet they have the variety which art demands; they have not the monotonous sameness of shape of the bricks in a wall. This is mainly due to the differences in the strains which cracked the original rock mass. So, from the beginning a sea-wall built by nature is more picturesque than a sea-wall built by man. And it goes on taking more and more picturesque shapes under the hammers of the waves. For the force of the waves, the angles at which they strike, the size and shape of the rock fragments with which they strike, these vary infinitely. ETCHING, SCULPTURE, AND LANDSCAPE GARDENING