If these layers were perfectly horizontal, laid one over another like the coats of an onion, we should have to dig through one before we could get to the second, and our knowledge of what the globe consists, would be much more limited than it is; for the greatest depth to which men have descended in the deepest mines, is not much greater than the thickness of one of the strata. But, instead of this, the surface is broken up by some force from beneath elevating portions, so as to form mountains and hills; and in consequence of this the edges of the strata appear on the surface one after another; just as you would see the edges of a row of bricks that had been set up on their ends, and then the last one thrown down so as to push down all the others. [Illustration] This is the way in which the strata are placed in the neighbourhood of Weymouth. [Illustration] The chief reason why I wished you to understand this is, that you may see how it is known that one stratum is older than another. It is evident that the substance marked _a_, in the section, which is limestone, must have been deposited before _b_, while _b_ must certainly be older than _c_. Now in most of the strata above the granite, which is nearly always in the position of the oldest formation, there are found various shells, plants, and bones of animals; and where certain remains of different animals or vegetables are found in one stratum, it is concluded that they must have been living about the same time. Most of the animals of the older strata were different in form from any at present known to exist; and some of them are very remarkable, and if they were alive now, would seem to us very strange and awkward. [Illustration: PLATE I EXTINCT ANIMALS.] CHAPTER II. WHAT CREATURES ONCE LIVED WHERE DORSETSHIRE NOW IS. I will show you a picture of what creatures were once living where the town of Lyme Regis, in Dorsetshire, now stands, and tell you something about their structure and their habits. You may perhaps be ready to think that a great deal of what we profess to know concerning them, is the work of fancy, but I can assure you it is not, and by and by I will endeavour to convince you that there is reason enough for you to believe what I tell you. THE ICHTHYOSAURUS. That large animal lying on the ground, is called the _Icthyosaurus_, from two Greek words signifying _Fish-Lizard_, in consequence of his possessing some of the peculiarities of both fishes and lizards. The usual length of this creature was from twenty to thirty feet. It possessed a most surprising combination of the powers and qualities of different animals which are now in existence. In its general form and character it must have been something like the modern porpoise; but it had the teeth of a crocodile, the head of a lizard, the back-bone of a fish, and the fins or _paddles_, of a whale.