Page:Catholic Encyclopedia, volume 11.djvu/455

 PALSONTOLOGY

411

PALEONTOLOGY

have their hollow chambers filled with a mineral sub- stance and afterwards the outer shell is chemically removed, so that only a cast of the inside or a hard kernel remains. Finally, the tracks of birds and rep- tiles, and traces of the trails of Crustacea and worms which have been preserved as impressions are counted as fossils. These are often found with the remains of moUuscs, as the well-known impressions of medusiE in the lithographic slate of Bavaria.

The study of palfeontological objects is often at- tended with great difficulties as for the most part the remains found are incomplete and their correct in- terpretation requires careful comparison with living organisms. Palaeontology, therefore, makes use of the methods of zoology and botany, but its task is a far more difficult one. In the fossils of animals all the fleshy parts are lacking, and even the hard parts are often enough only very imperfectly represented, and preserved in fragments. Ihe blossoms of plants are completely wanting, while leaves, fruit, stem, and root are hardly ever found together. Consequently, pate- ontologists have given special attention to the study of the comparative anatomy of the hard parts of organisms, and thus discovered important organic laws; among these should be especially mentioned Cuvier's "law of correlation". By this is meant the mutual dependence of the different parts of an organ- ism, which enables us, e. g., from the teeth alone, to decide whether an animal was carnivorous or herbiv- orous etc. Furthermore, by the aid of palaeontology the material of the biological sciences was enlarged to an astonishing degree, and many gaps therein were filled. The problems of the development theory re- ceived much light from the same source. Finally palseogeography is wholly dependent on this science, as the fossils indicate where there were continents and oceans, where the animal life of the coast developed, where coral reefs grew, where lakes containing fresh water organisms existed, where the primeval tropical forests flourished, and where the tundras of the cold regions extended. This not only enables us to fill the outlines of ancient continents and oceans, but also furnishes the means of determining the geographical distribution of plants and animals, and the climatic conditions during the different geological eras.

Of special importance is the historical side of paleontology. As has already been said, William Smith was the first to recognize the importance of fos- sils for the historical investigation of the earth's strata. Before his day they were regarded as proofs of the Flood. The greater part of the surface of the earth consists of varying stratified rocks that have been deposited by the ocean, by brackish, and by fresh water. Geology studies the individual strata and infers their age from their succession. This can easily be done in a limited district, but if two districts somewhat distant from each other are compared, then it will prove impossible by geology alone to establish that the two strata are of the same age, for at the same time in one place limestone may have been deposited, in another sandstone, and in a third clay. Again, strata of an epoch which appear in one place may bo wanting in another. In such cases the geologist may receive great assistance from palaeontology. For the stratified portion of the earth generally contains fos- sils which are found more or less frequently, whicl] arc so distributed that each group of strata ci>nrs|i(incl-; to a definite collection of species that hved when iIksc strata were deposited. In .such a case palaMiiitcilogy determines the chronological succession of the several fauna and flora and studies the mutual relations of the organic remains found at the different localities. By this means the contemporaneousness of the various strata may be recognized or the parallelism of the several strata established. In doing this, however, many obstacles have been overcome with considerable difficulty. Most strata have been deposited by the

sea. At the same time, however, deposits were formed by lakes; on land forests grew and land ani- mals lived, in warm seas there were luxurious growths of coral. Naturally each of these regions produced organisms utterly different; consequently some lucky discovery such as that of shells which found their way into deposits of plants, or that of the bone of a mam- mal imbedded in the sea-sand is required, in order to be able to decide whether the deposits are contem- poraneous. From what has been said it is clear that all fossils are not equally important and useful in determining the age of strata. Thus, all remains of land and fresh-water organisms are of less importance, because most strata were deposited by the ocean. Even the marine fossils are not all equally important. The most important are those combining the most rapid changes in character with the most extensive geographical distribution.

The most important task of pateontology is the in- vestigation of the history of the development of life, for it is the only science which furnishes means and in the fossils offers documents to elucidate this prob- lem. Only in this way is it possible to learn whether the past and present organisms form a continuous whole, or whether the fauna and flora of the various periods in the earth's historj- were destroyed by catastrophes and were replaced by a new creation. There ure two fundamental characteristics of all or- ganisms: heredity and variation. It is, at the same time, interesting to prove that the conception of mutation and with it of the evolution of living beings is older than the knowledge of its capacity of persist- ence. Aristotle believed that eels sprang from mud, Theophrastus accepted the belief that the tubers of a number of plants were formed from the earth, and even Goethe maintained the ojiinion that plant-lice were developed from parts of the plants. With Lin- naeus began the perception of the great importance in physical law of the capacity of persistence in organ- isms, which makes it possible for the naturalist to organize the whole of the great kingdom of living beings into genera and species. Darwin was as the opponent of Linnaeus, in that he once more brought the capacity for mutation of all organisms into the focus of natural philosophy.

According to the theory of the evolutionist all life issued from several cells, or according to some from a single cell. Of this cell, of course, no fossilized traces can have been preserved. Yet according to this theory we should expect the most ancient strata to be filled with the remains of animals and plants of the lowest type capable of preservation. This, how- ever, is not the case. In the Cambrian, the olilest stratified formation, which has yielded somewhat abundant fo.ssils, all families of the animal kirgdom are found, with exception of the vertebrates; all plants are likewise missing. These two groups first appear in the Silurian formation. The organisms found in the Cambrian formation are not the lowest of their kind, the brachiopods, for instance, and the trilobites are as highly-organized as the present representatives of their species. In the same manner, vertebrates are represented in the Silurian formation by the trunk-fish or oslraciiihv, and the oldest known plants are the algm and the highly-organized ferns. Consequently the lowest classes are not the earliest.. When by the dis- covery of older remains the limits of life were traced further back, here also remains of higher organisms were founfl, so that even here we are very far removed from the beginnings of life. In attempting to find traces of the simplest organisms the Eozoon canadense played a great role imtil it was .seen that in the remains in question crystals of olivin or chrysolite, that had been converted into serpentine, had produced the il- lusion of an organic structure. Great importance was also .attached to the appearance of graphite in the earliest of strata, until Weinscheok proved, at least