95. The PRIMARY formations are so called because they are the oldest known to us: they are not necessarily the first-formed aqueous deposits. Dr Hutton said truly: There is no trace of a beginning, and no signs of an end. In the PRIMARY or PALÆOZOIC (ancient-life) formations are found the earliest traces of life. The forms as a rule depart very widely from those with which we are acquainted now. The _Laurentian_ rocks have yielded only one fossil--a large foraminifer named _Eozoon Canadense_. The _Cambrian_ formation contains but few fossils--crustaceans, molluscs, zoophytes, and worm-tracks. The _Silurian_ strata are often abundantly fossiliferous. All the great classes of invertebrates are represented, and fish remains also occur. The _Devonian_ and _Old Red Sandstone_ are also characterised by the presence of an abundant fauna. In the Old Red Sandstone are numerous fish remains; it appears to have been an estuarine or lacustrine deposit; the Devonian, on the other hand, was marine, like the Silurian and Cambrian. The _Carboniferous_ formation is the chief repository of coal in Britain. It consists of terrestrial, fresh or brackish water, and marine deposits. The fauna and flora of the _Permian_, which is partly a marine and partly a fresh-water formation, are allied, upon the whole, to those of the Carboniferous, but offer at the same time many contrasts. 96. The SECONDARY OR MESOZOIC (middle-life) formations contain assemblages of fossils which do not depart so widely from analogous living forms as those belonging to Palæozoic times. The _Triassic_ strata yield abundance of rock-salt. In Britain they contain very few fossils, but these are more abundant in the Triassic deposits of foreign countries. The oldest known mammals first appear in this formation. The _Jurassic_ formation is very highly fossiliferous. It is distinguished by the occurrence of numerous reptilian remains. Nearly all the beds of this formation are marine, but there are associated with these the remains of a forest or old land surface, and a considerable accumulation of estuarine or fresh-water deposits; impure coals also occur in this formation. The _Cretaceous_ strata are almost wholly marine, and chiefly of deep-water origin. But some land-plants are found, chiefly ferns, conifers, and cycads. Near the base of the formation occurs a great river deposit (Weald clay) with numerous remains of reptiles. 97. Among the oldest strata of the TERTIARY or CAINOZOIC (recent-life) division we meet with the _dawn_ of the existing state of the testaceous fauna--the _Eocene_ (_eos_, dawn, and _kainos_, recent) containing three and a half per cent. of recent species among its shells. The proportion of recent species increases in the _Miocene_ (_meion_, less, and _kainos_, recent), although the majority of the molluscs entombed in that formation belong to extinct species. In the _Pliocene_ (_pleion_, more, and _kainos_, recent), however, the extinct species are in a minority.