. Biology in America. Biology. !rhe Story of the Rocks 111. while the physicist is yet more extravagant, asking in the light of recent experiments on radium 1,600,000,000 years for the age of the earth since it attained its present diameter. So in rehearsing brietly the story of the roeks perhaps we cannot do better than employ the words of the old story books and say that "once upon a time" when the waters covered most of Nortli America and the earliest Lauren tian rocks of northeastern Canada were beginning to be lifted up above the sur- face of the sea, life prolj- ably came upon
. Biology in America. Biology. !rhe Story of the Rocks 111. while the physicist is yet more extravagant, asking in the light of recent experiments on radium 1,600,000,000 years for the age of the earth since it attained its present diameter. So in rehearsing brietly the story of the roeks perhaps we cannot do better than employ the words of the old story books and say that "once upon a time" when the waters covered most of Nortli America and the earliest Lauren tian rocks of northeastern Canada were beginning to be lifted up above the sur- face of the sea, life prolj- ably came upon the earth ill the form of unieelluhir plants and animals. But regarding the birth (f life the rocks are mute. We have no record of its advent or its cradle. Its earliest remains known are those of the Huronian period, where liuried beneath rock strata several miles in thickness are marine algie, radiolarians and the tubes and burrows of annelid worms. Following these there appeared in the Cambrian period all the principal branches of inverte- brate animals, with the trilobites, the cu- rious crustacean fos- sils resembling the modern king crabs, and so named from the two longitudinal grooves which divide the body into three parallel lobes, occu- jiying the dominant phice. Hence this period is known as the age of trihibites. Tlic "Ordoviciau" pe- riod, whicli succeeded the Cambrian, witnessed tlie rise of laud plants and corals, the marvelous nautilids, witli their chambered shells, and the armored "fishes" or ostracoderms. A Trilobite Original photograph from a specimen in the geological collection of the Uni- versity of North Dakota. Courfrsj/ of Dr. A. O. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Young, R. T. (Robert Thompson), b. 1874. Boston, R. G. Badger
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