MACKIE — FIRST TRAGUS OF THE SUCCESSION OF LIFE. 
383 
as have two sccd-loLes or cotyledons, as all forest-trees and skrubs, 
which also are characterized by the possession of true woody struc- 
ture, the mode of growth being by concentric external layers around 
the stem, hence the term by which they are denominated — E.ro/jnis. 
The vegetable kingdom is, however, very variously grouped on 
different and excellent principles by various authors ; but the gTOup- 
ing presented in the table below (Table III.) will be found sufficient 
for, and, we think, best adapted to, geological purposes. 
In our considerations of the lowermost of all fossiliferous rocks we 
have brought ixnder notice the first, or, at any rate, the oldest and 
most remote forms of created beings as yet brought to light by the 
researches of geologists. These, if we compare them with the posi- 
tions of the classes to which they belong in the tables of the animal 
and vegetable kingdoms, will be found to be not of the lowest grades. 
The Oldhamia, whatever it may really be, is certainly above the 
monad or the diatom, and some natm-alists have put it even as high 
as the Sertularidae ; the worm-holes indicate the existence of a more 
elevated class, the Annelida ; while fragments of trilobites carry us 
still higher in the articulate group. Neither are the obscure vege- 
table traces with which we are first presented at the bottom of their 
kingdom, but they rank at least as high as the cellular alg£e. 
No foraminifers nor sponges, no animals of the globular type, pre- 
sent their remains ; no traces of diatoms, lichens, or fungi appear. It 
may be said these were too perishable in their natm-e to be pre- 
served. True some might have been so ; bvit othei'S were not, for in 
rocks less remote in age, diatoms, sponges, and foraminifers abound. 
When in Shrop-shii-e we pass away from the Longmynds and reach 
the well-kno^\'n Stiper-stones ; or when in "Wales, as at Harlech, we 
pass from the Cambrian grits to the " Lingnila-flags," fossils become 
more abundant and more diversified. We have then entered into 
another phase of the great Palaeozoic age, and new life-forms appear. 
One of the.se, a bracliiopod {Limjula JDavisi!) takes rank still higher 
in the scale of life than any of the few forms met with in the " Bottom- 
rocks" and presents us with the first appearance of the molluscan 
type ; while it occurs in such abundance, and within such a zone-like- 
special range as to give a characteristic name to the rock-mass in 
which it is embedded. 
