On the left hand side of the section the strata are so divided as to correspond to the six great groups of animals and plants that have appeared on the globe. The names attached to the groups are derived from [Greek: zôos] (_vivus_, living,) with the Greek numerals prefixed. The lowest group, being destitute of organic remains, is called _azoic_, (from [Greek: a] privitive and [Greek: zôos],) that is, wanting in the traces of life; and corresponds to the crystalline group on the other side of the section, embracing gneiss, mica slate, limestone, and clay slate, of unknown thickness. The _protozoic group_ corresponds to the palæozoic of the right hand side, and embraces lower and upper Silurian, Devonian, or old red sandstone, the carboniferous group, and the Permian, or lower new red; the whole in Great Britain not less than thirty-three thousand feet thick. The _deutozoic group_ consists only of the triassic, or upper new red sandstone, and is only nine hundred feet thick, but marks a distinct period of life. The _tritozoic_ embraces the lias and oölite, with the Wealden, and is three thousand six hundred feet thick. The _tetrazoic_ consists of the chalk and green sand, one thousand five hundred feet thick. The _pentezoic_ embraces the tertiary strata of the thickness of two thousand feet. The _hectozoic_ is confined to the modern deposits, only a few hundred feet thick, but entombing all the existing species of animals.
Had space permitted, I should have put upon the section a reference to the most characteristic and peculiar mineral, animal, or plant, in the different groups. Thus the azoic group is _crystalliferous_, or crystal-bearing. The lower or Silurian part of the protozoic group is _brachiopodiferous_, _trilobiferous_, _polypiferous_, and _cephalopodiferous_; that is, abounding in brachiopod and cephalopod shells; in polypifers, or corals; and in trilobites, a family of crustaceans. The middle part, or the Devonian, is _thaumichthiferous_, or containing remarkable fish. The upper part, or the coal measures, is _carboniferous_; that is, abounding in coal. _The deutozoic group_ is _ichniferous_, or track-bearing, from the multitude of its fossil footmarks. The _tritozoic group_ is _reptiliferous_, or reptile-bearing, from the extraordinary lizards which abound in it. The _tetrazoic_ is _foraminiferous_, from the abundance of coral animalcula, called foraminifera, or polythalmia, which it contains. The _pentezoic_ is _mammaliferous_, because it contains the remains of mammalia, or quadrupeds. The _hectozoic_ is _homoniferous_, or man-bearing, because it embraces human remains.