together with the submergence beneath the sea of a large portion of Northern and Western Europe.*

50. RETROSPECT; BOTANICAL EPOCHS.-I will conclude this discourse with a review of the prevailing botanical characters during the principal geological epochs.

Count Sternberg, M. Adolphe Brongniart, Dr. Lindley, and other eminent botanists have adduced some interesting generalizations from the fossil floras of the various formations: and although conclusions of this kind must be regarded in the nature of shifting hypotheses, and will require to be modified by new discoveries—for all the fossil species at present known amount only to about two thousand,† yet the characters of the floras of certain formations differ in so striking a manner from those of others, that it is very improbable that many of the essential features have been lost.

The flora of the ancient world may be regarded as characteristic of three distinct eras. The first period, termed by Brongniart "the age of Acrogens," comprehends the earliest strata in which traces of vegetation appear, and includes the Carboniferous. The plants of this epoch consist of fucoids, ferns of various kinds in great abundance, coniferous trees related to species of warm climates, cycadaceæ, a few flowering plants,§

* See also A. Henfrey's "Vegetation of Europe," for some valuable remarks on this subject.

+ Prof. Göppert, in 1845 (Rep. Brit. Assoc.), computed the number of species of fossil plants then known to amount to nearly 2000; and stated their distribution in the strata to be as follows:

Lycopodiaceous seed-vessels and fragments of wood, found in the Upper Silurian Tilestones, are the oldest-known terrestrial plant-remains. -H. E. Strickland, Quart. Journ. Geol. Soc. vol. ix. p. 10; and J. W. Salter, ibid. vol. xiv. p. 76.

§ The Antholites of the coal-measures. Some, at least, of these may have belonged to monocotyledonous, or even dicotyledonous, flowering plants, such as the Bromeliacea or the Lobeliaceæ. See Lindley and

great woody equisetaceæ, gigantic lycopodiaceæ, and trees (Sigillariæ) whose precise relations to known forms is not determined. In this flora the tree-ferns predominate, and the general type of the vegetation is analogous to that of the islands and archipelagos of tropical and subtropical climates

The second period (that of Gymnosperms) extends from the Triassic or New Red to the Chalk inclusive, and is characterized by the occurrence of many species of cycadaceae and coniferæ, a few palms, and, in the Lias,* of a few, but in the Cretaceous beds (see vol. i. p. 329) of many, dicotyledonous plants; while the proportion of ferns is much less than in the preceding period, and the lycopodiaceae and equisetaceæ are fewer, and present forms different to those of the carboniferous strata. A flora of this nature corresponds with that of the coasts and maritime districts of New Holland and the Cape of Good Hope.

The third epoch (Brongniart's " age of Angiosperms") is that of the tertiary, in which the dicotyledonous tribes present themselves in great abundance; the cycadaceae are rare, the ferns in diminished numbers, and the coniferæ and palms numerous.

In the latest tertiary strata are imbedded the remains of trees and plants of species still living in the countries where these deposits occur; and so also in the beds in actual progress of formation, the most delicate vegetable remains are preserved; thus, in the lacustrine marls of Scotland the leaves and seed-vessels of the Charæ are found in a state of fossilization scarcely distinguishable from the gyrogonites of the tertiary strata of the Paris basin, and of Headon Hill, or of the Purbeck beds of Dorsetshire.

From this review of the botanical epochs which the present state of geological knowledge enables us to establish, we perceive that, from the most ancient formation in which traces of vegetation remain, the sea has supported the usual forms of marine plants; and that on the land, ferns, other cryptogamia, and coniferæ have existed through periods of indefinite duration to the present time; the most striking and important differences in the ancient and modern floras being the numerical preponderance of the cryptogamia in Hutton's "Fossil Flora; " Morris, in Prestwich's Memoir on Coalbrook Dale, Geol. Trans. 2nd ser. vol. v.; and Hooker, in Lyell's "Manual" (Supplem. 1857).

* Buckman, Quart. Journ. Geol. Soc. vol. vi. p. 517.

the former, and of the dicotyledonous tribes in the latter,— and the more extensive geographical range of the same species of plants during the Carboniferous era. The theory of the progressive development of creation receives no support from the state of vegetation in the early geological epochs; not only the most perfectly organized of the cryptogamic class, but the coniferæ * also are among the oldest of fossil plants.

The absence of nearly all vegetable forms in the most ancient fossiliferous rocks must not be regarded as a proof that the floras of those remote periods were thus sterile; the only legitimate inference, in the present state of our knowledge, is, that the circumstances under which those strata were accumulated were unfavourable to the envelopment and preservation of terrestrial plants. We have seen that the grand fundamental distinctions of the vegetable kingdom existed in the early secondary ages, a fact in accordance with what we observed in the animal kingdom: and thus the same unity of purpose and design is manifest in all the varied forms of organization that lived on our planet through the vast periods of time which geological investigations have enabled us to scan.

See Dr. Hooker's opinion of the rank of conifers in the vegetable kingdom, Lyell's "Manual," 5th edit. p. 373.

LECTURE VIII.

PART I. THE DEVONIAN, SILURIAN, AND CAMBRIAN FORMATIONS.

7.

1. Introductory. 2. The Devonian Series. 3. Subdivisions of the Devonian Series,Herefordshire and Ireland. 4. Devonian Strata of Devonshire and Cornwall. 5. Devonian Strata of Scotland. 6. Devonian Strata of the Continent and America. Organic Remains of the Devonian Series,-Plants, Zoophytes, Molluscs. 8. Devonian Crustaceans. 9. Devonian Fishes and Reptiles. 10. The Silurian and Cambrian Rocks. 11. Silurian and Cambrian Strata of the British Isles. 12. The Longmynd or Bottom Rocks. 13. Silurian Strata of Staffordshire. 14. The Clent Hills. 15. The Wrekin. 16. The Malvern Hills, &c. 17. Silurian and Cambrian Strata of Europe and America. 18. Silurian Fossils,-Plant-remains. 19. Silurian Zoophytes,-Echinoderms and Annelides. 20. Silurian Molluscs. 21. Silurian Crustacea. 22. Visual Organs of Trilobites. 23. Silurian Fishes. 24. Slate-rocks. 25. Review of the Lower Palæozoic Series.

1. INTRODUCTORY.—In the previous Lecture the Floras of the paleozoic ages constituted the principal subject of investigation. We examined the primeval forests of coniferæ, the groves of arborescent ferns, and jungles of Sigillariæ and Calamites, which clothed the surface of the soil in that remote period of the earth's physical history. The insects which fluttered among the tropical vegetation of the islands and continents of those periods, the reptiles of the swamps, and the fishes and crustaceans which inhabited the seas and rivers, were brought in review before us, and we contemplated their extraordinary forms and organization, as preserved by those natural processes

"Which turned the ocean-bed to rock,

And changed its myriad living swarms
To the marble's veined forms."

MRS. HOWItt.

We now advance another stage in our eventful progress; and again we have to investigate deposits that have been

accumulating for innumerable ages in the profound depths of seas fed by rivers and streams charged with the detritus of the countries over which they flowed, and imbedding the remains of the plants and animals that existed at the period of their formation. Again we shall find new forms of existence presented to our notice, differing from, but bearing an analogy to, the inhabitants of the waters which deposited the marine strata of the most ancient beds previously examined, yet altogether dissimilar from those of modern eras. In vain may we seek for the remains of the mammalia of the Tertiary period, of the molluscs, fishes, and reptiles of the Chalk, of the colossal oviparous quadrupeds of the country of the Iguanodon,—of the dragon-forms of the Oolite,—of the fish-like lizards of the Lias,—or of the tropical forests of the Carboniferous period,-all have disappeared; and, as the traveller, who ascends to the regions of eternal snow, gradually loses sight of the abodes of man, and of the groves and forests, until he arrives at sterile plains, where a few stunted shrubs alone meet his eye,-and, as he advances, even these are lost, and mosses and lichens remain the only vestiges of organic life, and these too at length pass away, and he enters the confines of the inorganic kingdom of nature;—in like manner the geologist, who penetrates the secret recesses of the globe, perceives at every step of his progress the existing types of animals and vegetables gradually disappear, while the relics of other creations teem around him; these in their turn vanish from his sight,other new strange modifications of organic structure supply their place, these also fade away,-traces of animal and vegetable life become less and less manifest, until they altogether disappear; and he descends to the crystalline rocks, where all evidence of organization is lost, and the granite, like a pall thrown over the relics of the former world, conceals for ever the earliest scenes of the earth's physical drama.