"The invisible things of him are clearly seen, being understood by the things that are made." "In contemplation of created things, -MILTON. "Nature hath made nothing so base, but can "And in that rock are shapes of shells, and forms Of creatures in old worlds, Whose generations lived and died ere man Appeared upon the scene." -Adapted from CRABBE. VI. READING THE GEOLOGICAL RECORD. WE propose in this discourse to see what kind of record geology can give us of life upon the earth. Formation of rocks. To that end we must speak first of certain rock formations; whence the material comes, how it is deposited, and what changes follow. And as nature's methods are very constant, if we determine the processes for one age we solve the problem for all ages. The formation of different kinds of rocks may be illustrated as follows. After a heavy rain, the water that flows along the streets of a country. village, where the conditions of nature are but slightly changed, will be turbid and muddy; moving more or less rapidly according to the descent of the ground, and carrying along sand, clay, gravel, and such refuse as may come in its way. Moreover, if the surface be uneven and the soil soft or friable, the hillsides will be furrowed out and partially washed away. As the rivulets from streets or hills collect in a valley, they will form a current of increased volume and force, that will still bear onward its accumulation of sediment. Sediment distributed. If, now, the stream enter a pond or lake the current will widen, and so lose its force, gathered and and this heterogeneous mass of material, will be assorted and distributed somewhat as follows. The heavier particles, that is, the gravel, will sink first and be deposited in a bed of comparatively narrow limits near the entrance of the stream. The sand, being lighter, will be borne farther out, till the current can carry it no longer, when it will sink, and in consequence be distributed over a wider surface and above the gravel. And if the quantity of sand and gravel be about equal, it is evident the layer of sand will be as much thinner than that of the gravel, as the area covered is greater. Then, again, the silt-finely comminuted clay, called dust when dry-being still lighter than sand, will be borne still farther out, and distributed in consequence over a still larger area than either of the others. And, now, when in process of ages these beds. of sedimentary deposits solidify-change to solid rock, the lower bed will be conglomerate, the middle one sandstone, and the upper slate. A similar process goes on, on a much larger scale in the |