In the physical world around us, we behold a perpetual strife between the two great principles of renovation and decay. Hills are insensibly crumbling into valleys; valleys are gradually cut down, and their debris transported to the sea. Our shores bear witness to the slow but ever onward march of the ocean, whether as shattered cliff's worn by the incessant lashing of the surge, or as sand-banks and submerged forests that represent the wolds and holms of our forefathers. We mark, too, how the sediment thus borne into the main is sowing "The dust of continents to be;" while the slow elevation of large tracts of country, or the sudden upheaval of others, shows us by how powerful an agency the balance of land and sea is preserved, and how sometimes the paroxysm of an hour may effect a mightier change than the wasting and decay of a thousand years. We choose to call these two principles antagonistic, because in their effects they are entirely opposite; yet there is no discordance, no caprice in their operation. Each works out its end, and the result is the harmony and stability of the face of nature. In the world of life, too, there seems to have been a double principle of decline and renewal. The natural tendency of species and genera, like that of individuals, has been towards extinction. Why it should be so we know not, further than that they are for the most part influenced by every change in physical geography. But they probably obey a still higher law which governs their duration, as the laws of vitality govern the life of an individual If we are but slightly acquainted with the agency by which the degradation of land is counter-balanced, we are still more ignorant of the laws that preserve the balance of life. Creation is a mystery, and such it must for ever remain. So, too, are the principles on which it has been conducted. We can but mark their results. We see new species appear from time to time in the upward series of the geological formations, but they tell not whence they came. Of two genera created together at the beginning, one ere long died out, but the other still lives; yet here there is assuredly nought like discordance or caprice. Nay, these two principles--death and creation--have been in active operation all through the ages, and the result is that varied and exquisitely beautiful world wherein we dwell.