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Hence toward the close of the Paleozoic the southern lands of the eastern hemisphere were invaded by great glaciers or perhaps by ice sheets like that which now shrouds Greenland. These Permian ground moraines are not the first traces of the work of glaciers met with in the geological record.
This is confirmed by a number of interesting facts that have lately come to our knowledge in connection with the embryonic development of the Ceratodus and Lepidosiren; they give us important information as to the stem-history of the lower Vertebrates, and therefore of our early ancestors of the paleozoic age.
The 'Mollusca'. In what sense is the living 'Waldheimia' less embryonic, or more specialized; than the paleozoic 'Spirifer'; or the existing 'Rhynchonellae', 'Craniae', 'Discinae', 'Lingulae', than the Silurian species of the same genera?
The objection that broad statements of this kind, after all, rest largely on negative evidence is obvious, but it has less force than may at first be supposed; for, as might be expected from the circumstances of the case, we possess more abundant positive evidence regarding Fishes and marine Mollusks than respecting any other forms of animal life; and yet these offer us, through the whole range of geological time, no species ordinally distinct from those now living; while the far less numerous class of Echinoderms presents three; and the Crustacea two, such orders, though none of these come down later than the Paleozoic age.
They divide the eras into four, viz.: 1, Proterozoic; 2, Paleozoic; 3, Mesozoic; 4, Cenozoic. All these "zoics" have to do with life. Proterozoic means before life, and signifies the rocks that contain no fossils indicative of life; Paleozoic signifies the most ancient forms of life; Mesozoic signifies "middle life" or those between the most ancient and the Cenozoic, or recent forms of life.
We will describe the Algonkian rocks of two typical areas. The formation of flat-lying sandstone which covers this buried land surface is proved by its fossils to belong to the Cambrian, the earliest period of the Paleozoic era.
Their rudimentary structures foreshadowed what their descendants were to be, and give some clue to the earliest vertebrates from which they sprang. Like those whose remains are found in the lower Paleozoic systems, all of these Devonian vertebrates were aquatic and go under the general designation of fishes.
In the Cretaceous the teleosts, or bony fishes, made their appearance, while ganoids declined toward their present subordinate place. The amphibians culminated in the Triassic, some being formidable creatures as large as alligators. They were still of the primitive Paleozoic types.
"A snag in the shape of extra hard rock," replied the tunnel contractor. "Briefly, Paleozoic rocks make up the eastern part of the Andean Mountains in Peru, while the western range is formed of Mesozoic beds, volcanic ashes and lava of comparatively recent date.
Paleozoic he might be, but it stung him that she should tell him so. She delivered his coup de grace unerringly. "Take my advice and let love-making alone, or if you must make love, do it as other gods do my messenger. Otherwise your Elysian dignity is in jeopardy. You are not the kind of man that women love, mon cher. Come, it is time that we joined the others."
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