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- The Evolution of Man, V.2 - 10/63 -
III. Mesolithic group, or mesozoic (secondary) group of strata : VIII. Jurassic : 21. Portland : Upper oolithic.
III. Mesolithic group, or mesozoic (secondary) group of strata : VIII. Jurassic : 20. Oxford : Middle oolithic.
III. Mesolithic group, or mesozoic (secondary) group of strata : VIII. Jurassic : 19. Bath : Lower oolithic.
III. Mesolithic group, or mesozoic (secondary) group of strata : VIII. Jurassic : 18. Lias : Liassic.
III. Mesolithic group, or mesozoic (secondary) group of strata : VII. Triassic : 17. Keuper : Upper triassic.
III. Mesolithic group, or mesozoic (secondary) group of strata : VII. Triassic : 16. Muschelkalk : Middle triassic.
III. Mesolithic group, or mesozoic (secondary) group of strata : VII. Triassic : 15. Bunter : Lower triassic.
II. Paleolithic group, or paleozoic (primary) group of strata : VIb. Permian : 14. Zechstein : Upper permian.
II. Paleolithic group, or paleozoic (primary) group of strata : VIb. Permian : 13. Neurot sand : Lower permian.
II. Paleolithic group, or paleozoic (primary) group of strata : VIa. Carboniferous (coal-measures) : 12. Carboniferous sandstone : Upper carboniferous.
II. Paleolithic group, or paleozoic (primary) group of strata : VIa. Carboniferous (coal-measures) : 11. Carboniferous limestone : Lower carboniferous.
II. Paleolithic group, or paleozoic (primary) group of strata : V. Devonian : 10. Pilton : Upper devonian.
II. Paleolithic group, or paleozoic (primary) group of strata : V. Devonian : 9. Ilfracombe : Middle devonian.
II. Paleolithic group, or paleozoic (primary) group of strata : V. Devonian : 8. Linton : Lower devonian.
II. Paleolithic group, or paleozoic (primary) group of strata : IV. Silurian : 7. Ludlow : Upper silurian.
II. Paleolithic group, or paleozoic (primary) group of strata : IV. Silurian : 6. Wenlock : Middle silurian.
II. Paleolithic group, or paleozoic (primary) group of strata : IV. Silurian : 5. Llandeilo : Lower silurian.
I. Archeolithic group, or archeozoic (primordial) group of strata : III. Cambrian : 4. Potsdam : Upper cambrian.
I. Archeolithic group, or archeozoic (primordial) group of strata : III. Cambrian : 3. Longmynd : Lower cambrian.
I. Archeolithic group, or archeozoic (primordial) group of strata : II. Huronian : 2. Labrador : Upper laurentian.
I. Archeolithic group, or archeozoic (primordial) group of strata : I. Laurentian : 1. Ottawa : Lower laurentian.
The primordial period falls into three subordinate sections--the Laurentian, Huronian, and Cambrian, corresponding to the three chief groups of rocks that comprise the archaic formation. The immense period during which these rocks were forming in the primitive ocean probably comprises more than 50,000,000 years. At the commencement of it the oldest and simplest organisms were formed by spontaneous generation--the Monera, with which the history of life on our planet opened. From these were first developed unicellular organisms of the simplest character, the Protophyta and Protozoa (paulotomea, amoebae, rhizopods, infusoria, and other Protists). During this period the whole of the invertebrate ancestors of the human race were evolved from the unicellular organisms. We can deduce this from the fact that we already find remains of fossilised fishes (Selachii and Ganoids) towards the close of the following Silurian period. These are much more advanced and much younger than the lowest vertebrate, the Amphioxus, and the numerous skull-less vertebrates, related to the Amphioxus, that must have lived at that time. The whole of the invertebrate ancestors of the human race must have preceded these.
The primordial age is followed by a much shorter division, the paleozoic or Primary age. It is divided into four long periods, the Silurian, Devonian, Carboniferous, and Permian. The Silurian strata are particularly interesting because they contain the first fossil traces of vertebrates--teeth and scales of Selachii (Palaeodus) in the lower, and Ganoids (Pteraspis) in the upper Silurian. During the Devonian period the "old red sandstone" was formed; during the Carboniferous period were deposited the vast coal-measures that yield us our chief combustive material; in the Permian (or the Dyas), in fine, the new red sandstone, the Zechstein (magnesian limestone), and the Kupferschiefer (marl-slate) were formed. The collective depth of these strata is put at 40,000 to 45,000 feet. In any case, the paleozoic age, taken as a whole, was much shorter than the preceding and much longer than the subsequent periods. The strata that were deposited during this primary epoch contain a large number of fossils; besides the invertebrate species there are a good many vertebrates, and the fishes preponderate. There were so many fishes, especially primitive fishes (of the shark type) and plated fishes, during the Devonian, and also during the Carboniferous and Permian periods, that we may describe the whole paleozoic period as "the age of fishes." Among the paleozoic plated fishes or Ganoids the Crossopterygii and the Ctenodipterina (dipneusts) are of great importance.
During this period some of the fishes began to adapt themselves to living on land, and so gave rise to the class of the amphibia. We find in the Carboniferous period fossilised remains of five-toed amphibia, the oldest terrestrial, air-breathing vertebrates. These amphibia increase in variety in the Permian epoch. Towards the close of it we find the first Amniotes, the ancestors of the three higher classes of Vertebrates. These are lizard-like animals; the first to be discovered was the Proterosaurus, from the marl at Eisenach. The rise of the earliest Amniotes, among which must have been the common ancestor of the reptiles, birds, and mammals, is put back towards the close of the paleozoic age by the discovery of these reptile remains. The ancestors of our race during this period were at first represented by true fishes, then by dipneusts and amphibia, and finally by the earliest Amniotes, or the Protamniotes.
The third chief section of the organic history of the earth is the Mesozoic or Secondary period. This again is subdivided into three divisions Triassic, Jurassic, and Cretaceous. The thickness of the strata that were deposited in this period, from the beginning of the Triassic to the end of the Cretaceous period, is altogether about 15,000 feet, or not half as much as the paleozoic deposits. During this period there was a very brisk and manifold development in all branches of the animal kingdom. There were especially a number of new and interesting forms evolved in the vertebrate stem. Bony fishes (Teleostei) make their first appearance. Reptiles are found in extraordinary variety and number; the extinct giant-serpents (dinosauria), the sea-serpents (halisauria), and the flying lizards (pterosauria) are the most remarkable and best known of these. On account of this predominance of the reptile-class, the period is called "the age of reptiles." But the bird-class was also evolved during this period; they certainly originated from some division of the lizard-like reptiles. This is proved by the embryological identity of the birds and reptiles and their comparative anatomy, and, among other features, from the circumstance that in this period there were birds with teeth in their jaws and with tails like lizards (Archeopteryx, Odontornis).
Finally, the most advanced and (for us) the most important class of the vertebrates, the mammals, made their appearance during the mesozoic period. The earliest fossil remains of them were found in the latest Triassic strata--lower jaws of small ungulates and marsupials. More numerous remains are found a little later in the Jurassic, and some in the Cretaceous. All the mammal remains that we have from this section belong to the lower promammals and marsupials; among these were most certainly the ancestors of the human race. On the other hand, we have not found a single indisputable fossil of any higher mammal (a placental) in the whole of this period. This division of the mammals, which includes man, was not developed until later, towards the close of this or in the following period.
The fourth section of the organic history of the earth, the Tertiary or Cenozoic age, was much shorter than the preceding. The strata that were deposited during this period have a collective thickness of only about 3,000 feet. It is subdivided into four sections--the Eocene, Oligocene, Miocene, and Pliocene. During these periods there was a very varied development of higher plant and animal forms; the fauna and flora of our planet approached nearer and nearer to the character that they bear to-day. In particular, the most advanced class, the mammals, began to preponderate. Hence the Tertiary period may be called "the age of mammals." The highest section of this class, the placentals, now made their appearance; to this group the human race belongs. The first appearance of man, or, to be more precise, the development of man from some closely-related group of apes, probably falls in either the miocene or the pliocene period, the middle or the last section of the Tertiary period. Others believe that man properly so-called--man endowed with speech--was not evolved from the non-speaking ape-man (Pithecanthropus) until the following, the anthropozoic, age.
In this fifth and last section of the organic history of the earth we have the full development and dispersion of the various races of men, and so it is called the Anthropozoic as well as the Quaternary period. In the imperfect condition of paleontological and ethnographical science we cannot as yet give a confident answer to the question whether the evolution of the human race from some extinct ape or lemur took place at the beginning of this or towards the middle or the end of the Tertiary period. However, this much is certain: the development of civilisation falls in the anthropozoic age, and this is merely an insignificant fraction of the vast period of the whole history of life. When we remember this, it seems ridiculous to restrict the word "history" to the civilised period. If we divide into a hundred equal parts the whole period of the history of life, from the spontaneous generation of the first Monera to the present day, and if we then represent the relative duration of the five chief sections or ages, as calculated from the average thickness of the strata they contain, as percentages of this, we get something like the following relation:--
I. Archeolithic or archeozoic (primordial) age : 53 : 6.
II. Paleolithic or paleozoic (primary) age : 32 : 1.
III. Mesolithic or mesozoic (secondary) age : 11 : 5.
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