the origin of these creatures, they represent families which have endured till now in the struggle for existence without either elevation or degradation. Here, again, we may formulate another creative law. In every great group there are some forms much more capable of long continuance than others. Lingula among the Brachiopods is a marked instance. [70] Probably of the genus Olenellus. But when, with Hicks, we surmount the mass of barren beds underlying these remains, which from its unfossiliferous character is probably a somewhat rapid deposit of Arctic mud, like that which in all geological time has constituted the rough filling of our continental formations, and have suddenly sprung upon us many genera of Trilobites, including the fewest-jointed and most many-jointed, the smallest and the largest of their race, our astonishment must increase, till we recognise the fact that we are now in the presence of another great law of creation, which provides that every new type shall be rapidly extended to the extreme limits of its power of adaptation. That this is not merely local is evidenced by the researches of Matthew and Walcott in the oldest Cambrian of America, where a similar succession occurs, but with this difference, that in the wider area presented by the American continent we find a greater variety of forms of life. Walcott records up to 1892 no less than 67 genera and 165 species in the oldest Cambrian of America. These include representatives of the Sponges, Hydroids, Corals, Echinoderms, Worms, Brachiopods, Bivalve and Univalve Mollusks and Crustaceans, or in other words, all the leading groups of invertebrate animals that we find in the sea at present. Of these the dominant group is the Crustaceans, including Trilobites, numbering one-third of the whole; and these with the univalve Mollusks and the Brachiopods constitute the majority, the other groups having comparatively few species. What a marvellous incoming of life is here! Walcott may well say that on the theory of gradual development we must suppose that life existed at a period far before the Cambrian--as far, indeed, as the Cambrian is before our own time. But this would mean that we know only half of the history of life; and perhaps it is more reasonable to suppose that when the conditions became favourable, it came in with a rush.