But, after all, how little do we know of these laws, which are only beginning to dawn on the minds of naturalists; and which the imperfections of our classification and nomenclature, and the defects in our knowledge of fossil species, render very dim and uncertain. All that appears settled is the existence of a definite plan, working over long ages, and connected with the most remarkable correlation of physical and organic change: going on with regular march throughout the Palæozoic, and then brought to a close to make room for another great succession. This following Mesozoic time must next engage our attention. We may close for the present with presenting to the eye in tabular form the periods over which we have passed. The table on page 187, and the diagram (page 179), mutually illustrate each other; and it will be seen that each age constitutes cycle, similar in its leading features to the other cycles, while each is distinguished by some important fact in relation to the introduction of living beings. In this table I have, with Mr. Hull,[AB] for simplicity, arranged the formations of each age under three periods--an older, middle, and newer. Of these, however, the last or newest is in each case so important and varied as to merit division into two, in the manner which I have suggested in previous publications for the Palæozoic rocks of North America.[AC] Under each period I have endeavoured to give some characteristic example from Europe and America, except where, as in the case of the coal formation, the same names are used on both continents. Such a table as this, it must be observed, is only tentative, and may admit of important modifications. The Laurentian more especially may admit of division into several ages; and a separate age may be found to intervene between it and the Cambrian. The reader will please observe that this table refers to the changes on the continental plateaus; and that on both of these each age was introduced with shallow water and usually coarse deposits, succeeded by deeper water and finer beds, usually limestones, and these by a mixed formation returning to the shallow water and coarse deposits of the older period of the age. This last kind of deposition culminates in the great swamps of the coal formation. [AB] "Quarterly Journal of Science," July, 1869. [AC] "Acadian Geology," p. 137. CONDENSED TABULAR VIEW OF THE AGES AND PERIODS OF THE PALÆOZOIC AND EOZOIC. Key to Symbols ### Tabulate and Rugose Corals, abundant. *** Age of Algæ. === Age of Acrogens and Gymnosperms. +++ And God said, "Let the waters bring forth abundantly the swarming living creatures." --- And God created great reptiles. TIMES. AGES. PERIODS. ANIMALS AND PLANTS. PALÆOZOIC