"The first aspect of the globe which the investiL'a- tions of the cosmogonist have enabled us to realize, present to view a viscid igneous ball revolviuiij on its axis, and wheeling its annual course aroinid the sun, its centre of attraction. Its present oblate spheroid- ical form, flattened at the poles and elevated at the equator, is the exact form that a liquid sjihere of the size and weight of the earth, revolving on its axis in twenty-four hours, would assume ; and the still pre- vailing central heat, wdiich is indicated l)y the gradual increase of temperature as we descend in mines from the surface in the direction of the earth's centre, re- veals the igneous origin of the mass. The gradual cooling down of this fiery sphere, by radiation into space, would result in the formation of a crust of gran- ite or some other igneous rock on the surface ; and as the cooling progressed, the gases Mhich are the constit- uents of water, and which are kejit asunder by intense heat, would naturally combine, and thus the crust, in
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process of time, would be covered with an ocean. Thus we have all the elements requisite for the production of the first series of sedimentary rocks, which were formed out of the disturbed particles or detritus of the igneous crust at the bottom of the waters which encir- cled the globe. The lowest of our sedimentary rocks, gneiss and mica schist, which rest on the primordial granite, or some other rock of igneous origin, are found, on inspection, to be composed of the debris or broken particles of granite, and so far the foregoing theory of their origin is confirmed. This series of rocks has been styled 'metamorphic,' from the great change that has been wrought in their structure by the action of the intense heat to which, at the time of their fiirma- tion, they must have been exposed, and by which they have been partially crystallized, and their lines of stratification obliterated. They form a portion of that vast pile of the bottom rocks which have been termed ' the Cambrian,' and which have been calculated to be 25,000 feet, or nearly five miles, in depth or thickness.
"Throughout the long ages occu|iied bj' the deposi- tion of the mass of sediment of which these bottom rocks are composed, the temperature of the globe must have been very high, though graduall}' becoming more cool; and the traces of animal life in them are ex- tremely rare and diflicult to detect and identifj'. The scanty fossil remains which have been discovered by the industry and research of the geologist, reveal no type of animal life of a higher order than the zoophyte (a creature partly of animal and partly of a vegetable nature), annelids, or sea-worms, and bivalve niollusks — all of them marine creatures devoid of the senses of sight and hearing; and with them have been found traces of fucoids or sea-weeds, but no land vegetation. In fact, all that has been discovered of organic matter in these rocks indicates a beginning of life at the time of their formation, and a beginning of life in the low- est and n-.ost humble of its forms.
"The long aera of the Cambrian formation was suc- ceeded bj- another as extensive, during which the rocks Avhich have been denominated 'the Silurian' were form- ed, by sedimentary deposits, to the depth (as some es- timate) of 80,000 feet. The fossil remains of animals tliroughout this formation are abundant, and disclose the zoology of the a;ra to have been confined to sub- marine invertebrates, zoophytes, mollusks, and crus- taceans ; and no vertebrate animal appears until the close of the sera, when the remains of fishes are found in the beds which lie immediatelj' at the top of the Silurian formation. Light to some extent must have pervaded the earth during this period ; for many of the mollusks, and all of the crustaceans, were furnished with eyes, some of them, as in the instance of the tri- lobite, of a peculiarly elaborate and perfect structure. It appears to be a law of nature, that animals whose entire existence is passed in darkness are either w holly devoid of the organs of sight, or, if rudimentary eyes are discoverable, the}- are useless for the jiurposes of vision, as exemplified in the animals of all orders, from the mollusk to the mammals, which have been discov- ered in the caverns of lllyria, in the caverns of South America, mentioned by Humboldt, in the Mammoth Cave of Kentucky, in deep wells, and in depths of the sea w here no raj^ of light can penetrate.
"The system that succeeded the Silurian was (hat in which the Devonian or Old-Red-Sandstone rocks were formed ; and all geologists concur in stating that the position in which these rocks are found indicates that the a'ra was ushered in by violent commotions, during which most of the principal mountain ranges in the world were thrown up. The fossil remains of this era, during which sedimentary rocks, calculated to be about Hi, 000 feet in thickness, were formed, pre- sent to our view, in addition to the previous existing orders of animals, vertebrate fish of the Placoid and Ganoid species. These have been graphically de- scribed by Hugh Miller, in The Old Red Sandstone, as