« AnkstesnisTęsti »
some of the most important truths connected with the past history of our planet.-The great discoverer of those general laws of the animal kingdom was the illustrious French naturalist, the Baron Cuvier. He has shown, that there reigns such a harmony throughout all the parts of which the skeleton is composed, so nice an adaptation of the forms to the wants and habits of the animal, and such a degree of mutual subordination between one part and another in portions of the structure apparently quite unconnected, that we are enabled, by the inspection of a single bone, to say with certainty that it must have belonged to a particular kind of animal, and could not have formed a part of the skeleton of any other. Thus, if we present to a skilful comparative anatomist a small bone of the foot of a quadruped, he will not only pronounce with certainty as to the size of the animal, to which it belonged, but will say what sort of teeth it must have had— whether it had horns, and whether it fed upon the flesh of other animals, or on vegetable substances. If many detached bones belonging to the same kind of animal be collected, the skill of the comparative anatomist enables him to put them together in their true places; and thus a complete skeleton has been constructed of of separate fossil bones, which had belonged to several individuals of the same species. In this application of anatomy to geology we have a beautiful illustration of the intimate connexion of the sciences with each other. The discovery, in one of our stone quarries, of a few mutilated fragments of bone, imbedded in the solid rock, reveals to us the kind of animals that must have inhabited this region of the earth at the remote period when the rock was in the act of being deposited at the bottom of the sea, and tells us also that the climate was not that of the temperate zone, but of the tropics.
The most remarkable of the fossil saurians, which are found in the secondary strata, are those which have been called ichthyosaurus, plesiosaurus, megalosaurus, and iguanodon. The first of these is so called from the characters of the animal, partaking at the same time of the nature of a fish and of the lizard tribe;
ichthys and sauras being two Greek words signifying fish and lizard. Its head resembles that of a crocodile, only it is much larger and sharper, its snout ending in a point, almost as acute as the beak of a bird: it has a most formidable supply of sharp conical teeth, no less than sixty in each jaw. Its head was of an enormous size, for jaws measuring eight feet in length have been found; and it was furnished with a pair of eyes of still more extraordinary proportion, for the oval hollows for that organ, in a skull in the possession of a gentleman at Bristol, measure fourteen and a half inches in their largest diameter, the size of a dish on which a tolerably good-sized turkey could be served up. The head was about a fourth of the whole length of the animal, and was joined to the body by a very short neck: the back-bone was composed of joints or vertebræ different from those of land animals, and similar to those of fishes; it was supplied with four paddles like those of a turtle, in the lower part of the body, and by means of these, and its very powerful tail, it must have darted very swiftly through the water. It was a most singular combination of forms, for it had the snout of a dolphin, the teeth of a crocodile, the head and breast-bone of a lizard, extremities like the marine mammalia, and vertebræ like a fish.
We can, however, form no idea of the appearance of the animal when alive, except such as is conveyed to us by the sight of the skeleton; a very imperfect one, no doubt, as we know by the difference between any animal and its skeleton placed beside it. The foregoing representation of the complete skeleton of the ichthyosaurus, as restored in the way we have alluded to, is given by the Rev. W. Conybeare, the eminent geologist, to whom we are indebted for the most complete account of these fossil saurians.
Remains of the ichthyosaurus have been found in all the secondary strata, between the red sand-stone and the chalk, in many parts of England; but they are most frequently met with in the lias lime-stone, and in greatest abundance at Lyme Regis in Dorsetshire. They have also been found in several places on the continent, especially in Wurtemberg.
The plesiosaurus is so called from its near approach to the lizard tribe, plesion being Greek for near. It has a considerable resemblance in the body to the ichthyosaurus, but the head is much smaller, and is altogether of a different structure; but its most remarkable character is the great length of its neck. In man, all quadrupeds, and other mammalia, there are exactly seven joints or vertebræ in the neck; and so strict is the adherence to this rule, that there is precisely the same number in the short, stiff neck of the whale, and the long, flexible neck of the giraffe. Reptiles have from three to eight joints-birds many more: the swan, which has the most, is enabled to make the graceful curves of its neck by being provided with twenty-three of those separate vertebræ; but the plesiosaurus had no less than forty-one.
Mr. Conybeare, to whom we are indebted for the first description and name of the plesiosaurus, has given the following representation of this extraordinary longnecked reptile, in a restored state, in the same way as he has given us a figure of the ichthyosaurus.
Some fragments of the bones of a saurian of gigantic size were discovered by Dr. Buckland, a few years ago, in the quarry of Stonesfield, near Woodstock, in Oxfordshire. According to the opinion of Cuvier, who examined them, they must have belonged to an individual of the lizard tribe, measuring forty feet in length,
and having a bulk equal to that of an elephant seven feet high. This fossil animal was distinguished by Dr. Buckland with the name megalosaurus, on account of its great size, megale being Greek for great.
A most curious discovery was made a few years ago by Dr. Buckland at Lyme Regis.
He had often remarked a number of long rounded stony bodies, like oblong pebbles or kidney potatoes, scattered on the shore, and frequently lying beside the bones of the saurians when these were discovered in the rock. He was induced to make a closer examination of them, and they turned out to be the dung of the saurian reptiles in a fossil state. When found along with the bones they are always under or among the ribs. Many specimens of them contained scales, teeth, and bones of fishes that seemed to have passed undigested through the body of the animal; just as the enamel of teeth and fragments of bone are found undigested in the dung of the ravenous hyæna. It was thus shown, that these great monsters of the deep fed not only on their weaker neighbours, but sometimes even on the smaller defenceless individuals of their own species; for Dr. Buckland found in one of these stone: a joint of the back-bone of an ichthyosaurus, that must have been at least four feet in length. He has calle the stones coprolites, from kopros, Greek for dung, and lithos, a stone. Since his attention was directed to the subject, he has found similar bodies in many other strata, and belonging to different animals. "In all these various formations," he says, "the coprolites form records of warfare waged by successive generations of inhabitants of our planet on one another; and the general law of nature, which bids all to eat and to be eaten in their turn, is shown to have been co-extensive with animal existence upon our globe; the carnivora in each period of the world's history fulfilling their destined office to check excess in the progress of life, and maintain the balance of creation."
HISTORY AND CHRONOLOGY.
History is the record of public events that have occurred in different ages and nations. Chronology treats of the precise dates at which these events took place. Our knowledge of historical events is derived chiefly from the writings of individuals; but these are aided by public records, inscriptions, coins, and other documents of a similar nature. Our knowledge of the chronology of these events is drawn from similar sources. History and Chronology therefore are intimately connected; yet they are so distinct as to suggest very different trains of investigation, History treats of the characters of the persons engaged in the events which it records, the motives which influenced them, the circumstances which led to the events, the incidents which accompanied them, the effects which resulted from them, involving considerations of the state of the nations that were engaged in them, their advancement in civilization and useful arts, and their relative position with respect to one another. The study of chronology, on the other hand, leads to the examination of the divisions of time that have prevailed in different nations; their modes of reckoning hours, days, weeks, months, years; different epochs that have been used in different ages and nations; cycles and other periodical revolutions of years; the deciphering of the devices and legends of coins and medals, the calculating of the eclipses that are mentioned in connexion with historical events; and, in short, the investigating and estimating of any notices of time that may be discovered either in natural objects, or in any record kept by men of the transactions in which they have been engaged.