Imágenes de páginas
PDF
EPUB

could have operated with sufficient power to remove all traces of their former existence. The characteristic plants of the coal age, now declining, were replaced by cycads and many new forms of conifers and ferns. The cycad was intermediate in character, resembling the fern in the opening of its foliage, and the palm in its general habits. It was now in the full zenith' of its expansion, while the fern was dying out and the conifer was yet to be developed. More than 100 angiosperms made their appearance, one-half of them closely allied to the trees of modern forests and the fruit trees of temperate regions. In the latter part of the age the palm, at present the most perfect type of the vegetable kingdomn, was also introduced. New animal species made their appearance, attended by the extinction of all pre-existing forms. Reptiles now reached their culmination, the earth, sea and air, each having its peculiar kind. Their fossil remains indicate a large number of both berbiverous and carniverous species, which in many instances attained a length of 60 feet. The ichthyosaurus, a prominent example, united in its structure parts of several related animals, having the head of a lizard, the snout of a porpoise, the teeth of a crocodile, the spine of a fish and the paddles of a whale. Its eyes, enormously large, were arranged to act both like the telescope and the microscope, thus enabling it to see its prey both night and day, and at all distances. It subsisted on fish and the young of its own species, some of which must have been swallowed several fcet in length. Associated with it was the Pleiosaurus, an animal resembling it in its general structure. A remarkable difference, however, was the great length of neck possessed by the latter, which contained 40 vertebræ, the largest number that has ever been found in animals living or fossil. These two reptiles for a long time ruled the seas and kept the increase of other animals within proper limits. But the most gigantic of reptile monsters was the Iguanodon. Some individuals were 60 feet long, 15 feet round the largest part of the body, had feet 12 feet in length, and thighs 7 feet in diameter. The most heteroclitic creature was the Pterodactyl. It had the neck of a bird, the mouth of a reptile, the wings of a bat, and the body and tail of a mammal. Its curi

us organization enabled it to walk on two feet, fly like a bat, and creep, climb or dive in pursuit of its food. The age is also remarkable as the era of the first mammels, the first birds, and the first common fishes.

The Mammalian Age witnessed the increase of the mass of the eart! above the ocean's level three-fold. The world-constructing architect, the coral insect, built up Florida out of the sea, thus completing the southern expanse of the continent. Its eastern and western borders were substantially finished, and superficially its great plateaus, mountain chains and river systems, approximated their present geographical aspects. The Rocky Mountains were elevated to a hight of 7,000 feet, the Wind River chain 6,800, the Big Horn Mountains 6,000, Pike's Peak 4,500. The upheaval of the Rocky Mountain region greatly enlarged the Missouri, previously an inconsiderable stream, adding to it the Yellowstone, Platte, Kansas and other tributaries. The Lower Mississippi was formed and discharged its vast volume of accumulated waters near the present coast line of the Gulf. The elevation of mountain masses to snowy altitudes cooled down the temperature and introduced

[ocr errors]

substantially the present climates. In Europe the change was gradual from tropical to subtropical and temperate; in North America abrupt. As a consequence the botany of the latter opened with the oak, poplar, dogwood, magnolia, fig, palm and other plants closely resembling those of the present day.

Of the animals the Mammoth was remarkable. Unlike the elephant of the present day, they were covered with a redish wool intermingled with hair and black bristles, the latter being more than a foot in length. Vast herds of these huge creatures, nearly three times as large as the present elephant, their living representative wandered over the northern part of both hemispheres. An individual in a perfect state of preservation was found in 1790, encased in ice, at the mouth of the river Lena. It still retained the wool on its hide, and otherwise was so free from decay, that its flesh was eaten by dogs. Their remains are abundantly distributed over the northern part of the United States, imbedded usually in marshes where the animals were perhaps mired while in search of food or water. A large fossil specimen was recently exhumed in Macon county, Illinois, 2 miles southeast of Illiopolis, in the edge of Long Point Slough, by the side of an oozy spring. The fossils have been found in other localities of the State, and the prairies may have been places of frequent resort. Contemporaneous with them were the Dinotherium and Megatherium, and other creatures of the most gigantic proportions. The magnitude of the Mammoth seems almost fabulous, but that of the Dinotherium probably surpassed it. One of its most remarkable features was its enormous tusks, projecting from the anterior extremity of the lower jaw, which curved down like those of the walrus. Like the rhinoceros, it lived in the water, and was well adapted to the lacustrine condition of the earth common at the time it flourished. The Megatherium, belonging to the sloth family, was also of colossal dimensions. Its body, in some instances 18 feet long, rested on legs resembling columns of support rather than organs of locomotion. Its spinal column contained a nerve a foot in diameter; its femur was three times the size of the elephant's, while its feet were a yard in length and more than a foot in width. The tail near the body was two feet in diameter, and used with its hind legs as a tripod on which the animal sat when it wielded its huge arms and hands.

Toward the close of the age oscillations occurred in the northern part of the continent, greatly modifying the condition of its surface. During the upward vibration vast glaciers spread over British America and the contiguous portion of the United States. These fields of ice, becoming filled with hard boulders, and moving southward by expansion, ground into fragments the underlying rocks. The sediment was gathered up by the moving mass, and when a latitude sufficiently warm to melt the ice was reached, it was spread over the surface. Accumulations of this kind constitute the drift which extends from New England westward beyond the Mississippi, and from the 39th parallel northward to an unknown limit. In Illinois, with the exception of small areas in the northwestern and southern parts of the State, it covers the entire surface with a varying stratum of from 10 to 200 feet in thickness. Here, and in other parts of the West, not only glaciers, but icebergs, were connected with its distribution. The waters of the

lakes then extended southward perhaps to the highlands, crossing the State from Grand Tower east toward the Ohio. This barrier formed the southern limits of this sea, and also of the drift which was distributed over its bottom by floating bodies of ice filled with sediment previously detached from the glaciers farther north. The upward movement of the glacial epoch was followed by a depression of the surface below its present level. The subsidence in Connecticut was 50 feet; in Massachusetts, 170; in New Hampshire, 200; at Montreal, 450; and several hundred in the region of Illinois and the Pacific. Previously the adjacent Atlantic seaboard extended into the sea beyond its present limits; now it receded, and the St. Lawrence and Lake Champlain became gulfs extending far inland. As the result of the down-throw the temperature was elevated, causing the glaciers to melt, and a further dissemination of the drift. Regular outlines, due to the dinamic forces, ice and water, were thus imparted to the surface, which a subsequent emergence brought to its present level. Order, beauty, and utility sprang into being and harmony with man, the highest type of terrestrial life, now in the dawn of his existence.

The Age of Man commenced with the present geological condi. tions. The great mountain reliefs and diversities of climate attending the present and the close of the preceding age, largely angmented the variety of physical conditions which modify vegetable and animal life. Multiplying under these diverse influences, the present flora exceeds 100,000 species. The palm alone, culminating in the present era, and standing at the head of the vegetable kingdom, embraces 1,000. Commensurate with the variety of plants is the extent of their distribution. They are found universally, from Arctic snows to Tropical sands, growing in the air and water, covering the land with verdure, and ministering to the wants of their cousins, the different forms of animal life. In the jungle the wild beast makes his lair; the bird builds her nest in their sheltering leaves and branches, and subsists on their fruits; and man converts them into innumerable forms of food, ornaments and material for the construction of his dwellings. In the oak and towering cedar their forms are venerable and majestic; graceful and beautiful in the waving foliage and clinging vine, and profoundly interesting in their growth and structure; crowned with a floral magnificence greatly transcending their predecessors of previous ages, they give enchantment to the landscape, sweetness to the vernal breeze, and refinement and purity to all who come within their influence. As in the case of plants, a diversity of physical conditions has impressed a inultiplicity and variety upon the animals. The approximate number of species at the present time is 350,000, each sub-kingdom numbering as follows: Radiates, 10,000; Mollusks, 20,000; Articulates, 300,000; Vertebrates, 21,000. Of the existing Vertebrates, Fishes embrace 10,000; Reptiles, 2,000; Birds, 7,000, and Mammals, 2,000. With the appearance of Man on the stage of being, in the latter part of the preceding age, many types of the lower animals, in which magnitude and brute ferocity were prominent characteristics, became extinct. Their successors, as if harmonizing with the higher life developing in their midst, were generally reduced in size, less brutal in their nature, and more active, beautiful and intelligent.

Recent discoveries have shown that the appearance of man, in. stead of being confined to the geological age which bears his name, must be extended back to an indefinite period. His remains and the relics of his art show that he was a contemporary of the mammoth; that he witnessed the inundation that buried the northern plains of the Old and New Worlds under the sea of ice; and that even before that time, when sub-tropical animals disported themselves in the forests of middle Europe, have traces of his existence been discovered. Though the absolute time of his advent cannot be determined, he doubtless was an inhabitant of the earth several hundred thousand years before he was sufficiently intelligent to preserve the records of his own history. His appearance as the head of the animal kingdom marks a new stage in the unfoldment of terrestrial life. His claim to this preeminence is based on the superiority of his mental, moral and spiritual endowments. Having an understanding capable of endless progression in knowledge, he is able to study the laws of nature and make them subservient to his will and wants; to institute systems of government for his protection, and to hold in subjection the lower animals, however greatly they may exceed him in size or physical strength. He is the only terrestrial being capable of comprehending the nature of moral relations; of distinguishing right from wrong, and of deriving happiness from the practice of virtue and suffering in consequence of vice. In his reverence for the Deity and aspirations for immortality he is removed still further from the animal plane, and stands as a connecting link between the latter and spirit existance.

The present age still retains, in a diminished degree of activity, the geological forces of previous periods. Extensive flats at many points along the Atlantic coast, and the deltas and other alluvial formations of rivers, are slowly extending the present surface. The latter, in many places, is becoming modified by the production of peat-beds; in volcanic regions, by the ejection of lava, and in paroxysmal disturbances, extensive areas are still subject to elevations and depressions, evidently a continuation of previous oscillations. As observed by Moravian settlers, the western coast of Greenland, for a distance of 600 miles, has been slowly sinking during the last four centuries. The border of the continent, from Labrador southward to New Jersey, is supposed to be undergoing changes of level, but more accurate observations will be necessary to determine the extent of the movement.

Like the uninterrupted course of human history there are no strongly drawn lines between the ages and their corresponding system of rocks and organic remains. Culminent phases occur, giving distinctiveness to the center of each and distinguishing it from others. The germ of each was long working forward in the past before it attained its full development and peculiar character, and extended far into the future for its decline and final extinction. There is, hence, a blending of periods and their products, and, while centrally well defined, their beginnings and endings are without lines of demarkation. The ratios, representing the comparative length of each age as determined by the thickness of its rocks and the rate of their formation, are as follows: Salurian, including the Laurentian and Huronian, 49; Devonian, 15; Carboniferous, 15; Reptilian, 23; Mammalian, 18. In consequence of the constantly varying conditions attending the growth of rocks, these results are only approximations to the truth.

They are, however, sufficiently correct to give the proportionate duration of these great geological eras, and will doubtless, by future research, be rendered more accurate. Could definite intervals of time bé substituted for these ratios, the most ample evidence exists to prove that the results would be inconceivably great. Even within the period of existing causes, the mind is startled at the tremendous sweep of ages required to effect comparatively small results. The waters of Lake Erie originally extended below the present Falls of Niagara, and the cataract, in subsequently passing from the same point to its present position, excavated the intervening channel of the river. Allowing the rate of movement to be one inch per year, which is perhaps not too low an estimate, it would require 380,000 years to pass over the six miles of retrocession. Judging from this estimate, what time would be required to excavate the canon of the Colorado, which is 300 miles long, and has been worn a large part of the distance through granite from 3000 to 6000 feet in depth. Captain Hunt, who for many years 'was stationed at Key West, and whose opportunity for observations was good, estimates that the coral insects, which have built up the limestone formations of Florida, must have required more than 5,000,000 years to complete their labors.

« AnteriorContinuar »