The Algonkian series embraces a great thickness of sedimentary beds, in part metamorphosed, which in certain localities rest unconformably on the eroded surface of the Basement Complex and in places are overlain unconformably by Cambrian rocks. Both the upper and lower contacts, however, in certain localities, have been rendered obscure by metamorphism. The system derives its name from a tribe of Indians that inhabited the region about the shores of Lake Superior, where it is well developed. The Algonkian terranes are exposed in the Grand Canyon of the Colorado, in the Wasatch and Uintah Mountains, the Black Hills of Dakota, about the southern shore of Lake Superior, and in many parts of eastern Canada, as well as in several other localities. The oldest known fossils occur in these rocks, and consist of a small number of brachiopods, molluscs, crustaceans, etc. These scanty records are suggestive, and at least stimulate the hope that an extensive pre-Cambrian fauna will ultimately be discovered. The few forms found seem to be not far different from the similar life records of the Cambrian. The Cambrian system, although first studied in Europe, has an important development in North America, and occurs at the surface at a large number of localities ranging from Newfoundland to California. The known distribution of the system and the nature of the rocks composing it indicate that it occurs widely in the Continental basin beneath subsequent deposits. The most interesting results derived from the study of the Cambrian, carried on especially by C. D. Walcott, pertain to its life records. With the exception of a few obscure algae, all the fossils thus far discovered are marine invertebrates. As regards rank in the zoological scale, certain molluscan remains are the highest, but outclassing them in size, abundance, and degree of specialization are the _trilobites_, the nearest living representatives of which are certain crustaceans. Of the trilobites about 100 species have been discovered in the Cambrian rocks of North America, the largest individual being about 20 inches in length. The picture of the continent which the facts just referred to enables one to sketch in fancy includes land areas destitute of animal life, and probably without vegetation, except perhaps the lichens, the lowest of the cryptogams. The sea, especially in its shallower portions near land and over its surface, contains algae, mostly, we presume, of small size, in fact microscopic, and soft tissued. The animal life subsisting primarily on the algae are all invertebrates, and nearly all of them, excepting the crustaceans, simple in organization. None of the animals the remains of which have thus far been discovered had strong shells or other well-developed protective or supporting tissues, thus indicating that they were not subject to the attacks of formidable enemies.