A notice of the life of Aristoteles as botanist and zoologist has already been given, and now a few words must be said about the opinions held by this very remarkable man regarding changes in the earth. He progressed beyond Pythagoras, for he refers to many examples of changes now constantly going on, and insists, emphatically, on the great results which they must produce _in the lapse of ages_. The changes of the earth, he says, are so slow in comparison to the duration of our lives, that they are overlooked, and the migrations of people after great catastrophes, and their removal to other regions, cause the event to be forgotten. In one work Aristoteles wrote: “The distribution of land and sea, in particular regions, does not endure throughout all time, but it becomes sea in those parts where it was land, and again it becomes land where it was sea; and there is reason for thinking that these changes take place according to a certain system and within a certain period. Everything changes in the course of time.” There was a great geographer called Strabo, about whose life little is known, except that he travelled far and wide in Europe and North Africa, and wrote largely on the earth. He did not content himself with simple geography, however, for he entered into a discussion, which was a very common one in those days, as it has been since, concerning the nature of the fossil shells which are found in strata or layers of the earth remote from the sea. He attributed the collecting of the shells where they are found to the former subsidence of the land, and not to the rising of the sea. It is not, he said, because the lands covered by seas were originally at different altitudes, that the waters have risen or subsided or receded from some parts and inundated others, but the reason is, that the same land is sometimes raised up and sometimes depressed, so that it either overflows or returns to its own place again. We must therefore ascribe the cause to the ground, either to that ground which is under the sea or to that which becomes flooded by it, but rather to that which lies beneath the sea, for this is more moveable, and on account of its humidity can be altered with greater celerity. This philosopher clearly laid down the law that the general level of the sea has remained the same, but that it has been and is the land which has been or is upheaved or subsided. It is a fundamental truth on which much of the science of geology depends. He moreover asserted that volcanoes were safety-valves, and were the result of subterranean convulsions.