of the upper reaches of that awful tide of continuity which had no beginning, and of which the measured shreds and fragments constitute time, we had become jealous lest even God himself should have wrought in it during other than a brief and limited space, with which our small faculties could easily grapple.

'Oh, who can strive

To comprehend the vast, the awful truth
Of the eternity that hath gone by,
And not recoil from the dismaying sense
Of human impotence! The life of man
Is summed in birthdays and in sepulchres,
But the eternal God had no beginning.'

There are two great infinites,-the infinite in space and the infinite in time. It were well, surely, to be humble enough to acknowledge it accordant to all analogy, that as He who inhabits eternity has filled the one limitless voidthat of space-with world upon world and system upon system, far beyond the reach of human ken, He should also have wrought in the other limitless world-that of time-for age after age, and period after period, far beyond the reach of human conception.

LECTURE FOURTH.

The Continuity of Existences twice broken in Geological History-The three great Geological Divisions representative of three independent Orders of ExistencesOrigin of the Wealden in England-Its great Depth and high Antiquity-The question whether the Weald Formation belongs to the Cretaceous or the Oolitic System determined in favour of the latter by its Position in Scotland-Its Organisms, consisting of both Salt and Fresh Water Animals, indicative of its Fluviatile Origin, but in proximity to the Ocean-The Outliers of the Weald in Morayshire-Their Organisms-The Sabbath-Stone of the Northumberland Coal Pits-Origin of its Name-The Framework of Scotland-The Conditions under which it may have been formed-The Lias and the Oolite produced by the last great Upheaval of its Northern Mountains-The Line of Elevation of the Lowland Counties-Localities of the Oolitic Deposits of Scotland-Its Flora and Fauna-History of one of its Pine Trees-Its Animal Organisms-A Walk into the Wilds of the Oolite Hills of Sutherland.

THE mystic thread, with its three strands of black, white, and grey, spun by the sybil in Guy Mannering, formed, she said, a ‘full hank, but not a haill ane:' the lengthened tale of years which it symbolized 'was thrice broken and thrice to asp.' I have sometimes thought of that wonderfully mingled and variously coloured thread of existence which descends from the earliest periods known to the geologist down to our own times, as not unaptly represented by that produced on this occasion from the spindle of the gipsy. We find, in its general tissue, species interlaced with and laying hold of species, as, in the thread, fibre is interlaced with and lays hold of fibre; and as by this arrangement the fibres, though not themselves continuous, but of very limited length, form a continuous cord, so species of limited duration, that at certain parts in the course of time began to be, and at certain other parts became extinct, form throughout

immensely extended periods a continuous cord of existence. New species had come into being ere the old ones dropped away and disappeared; and there occurred for long ages no break or hiatus in the course, just as in the human family there occurs no abrupt break or hiatus, from the circumstance that new generations come upon the stage ere the old ones make their final exit. But in the geological thread, as in that of the sybil, the continuity is twice abruptly broken, and the thread itself divided, in consequence, into three parts. It is continuous from the present time up to the commencement of the Tertiary period; and then so abrupt a break occurs, that, with the exception of the microscopic diatomaceæ, to which I last evening referred, and of one shell and one coral, not a single species crosses the gap. On its further or remoter side, however, where the Secondary division closes, the intermingling of species again begins, and runs on till the commencement of this great Secondary division; and then, just where the Paleozoic division closes, we find another abrupt break, crossed, if crossed at all,-for there still exists some doubt on the subject, by but two species. of plant. And then, from the further side of this second gap the thread of being continues unbroken, until we find it terminating with the first beginnings of life upon our planet. Why these strange gaps should occur, why the long descending cord of organic existence should be thus mysteriously broken in three,-we know not yet, and never may; but, like the division into books and chapters of some great work on natural history, such as that of Cuvier or Buffon, it serves to break up the whole according to an intelligible plan, the scheme of which we may, in part at least, aspire to comprehend. The three great divisions of the geologist, Tertiary, Secondary, and Paleozoic,―of which these two chasms, with the be

1

1 For a reference to the research of the last two years, which has been busily at work upon this precise epoch, see Preface.

ginnings of life on the one hand, and the present state of things on the other, form the terminal limits,-represent each, if I may so express myself, an independent dynasty or empire. Under certain qualifications, to which I shall afterwards refer, the Tertiary division represents the dynasty of the mammal; the Secondary division the dynasty of the reptile; and the Paleozoic division the dynasty of the fish. Each of the divisions, too, has a special type or characteristic fashion of its own; so that the aspect of its existences differs as much in the group from the aspect of the existences of each of the others, as if they had been groups belonging to different planets. The vegetable and animal organisms of the planet Venus may not differ more from those of the planet Mars, or those of Mars from the organisms of the planet Jupiter, than the existences of the Tertiary division differ from those of the Secondary one, or those of the Secondary one from the existences of the Paleozoic division.

Beneath the two great divisions of the Cretaceous system, and consequently of more ancient date, there occurs in the sister kingdom an important series of beds, chiefly of lacustrine or fluviatile origin, known as the Wealden. Before the submergence of what are now the south-eastern parts of England, first beneath the comparatively shallow sea of the Greensand, and then beneath the profounder depths of the ocean of the Chalk, a mighty river, the drainage of some unknown continent, seems to have flowed for many ages along those parts of Kent, Surrey, and Sussex, known as the Valley of the Weald. The banks of this old nameless river were covered with forests of coniferous trees of the Pine and Araucarian families, with cycadeæ and ferns, and were haunted by gigantic reptiles, herbivorous and carnivorous, some of which rivalled in bulk the mammoth and the elephant; its waters were inhabited by amphibiæ of the same great class, chiefly crocodiles and chelonians of extinct species and type; by numerous fishes, too, of the old

prey.

ganoid order; and by shells whose families, and even genera, still exist in our pools and rivers, though the species be all gone. Winged reptiles, too, occasionally flitted amid its woods, or sped over its broad bosom; and insects of the same family as that to which our dragon-flies belong spent the first two stages of their existence at the bottom of its pools and shallows, and the terminal one in darting over it gauze in on their wings of delicate of their quest It is stated by Dr. Mantell, our highest authority on the subject of the Weald, that the delta of this great river is about two thousand feet in thickness,-a thickness which quadruples that of the delta of the Mississippi. There can be little doubt that the American 'Father of Waters' is a very ancient river; and yet it would seem that this river of the Wealden, which has now existed for myriads of ages in but its fossilized remains, hidden under the Wolds of Surrey and Kent,—this old river, which flowed over where the ocean of the Oolite once had been, and in turn gave place and was overflowed by the ocean of the Chalk,-continued to roll its downward waters amid forests as dense and as thickly inhabited as those of the great American valley, during a period perhaps four times as extended.

Compared with the English formation of the Weald, which extends over a wide, and what was at one time a very rude district, our beds of the Scotch Wealden are but of little depth, and limited extent. And yet they serve to throw a not unimportant light on the true character and place of the formation. It occurs in England, as I have said, between two great marine systems, the Cretaceous and the Oolitic; and the question has arisen, to which of these systems does it belong? Now, our Scotch beds of the Weald determine the question. They make their appearance, not at the top of the Oolitic deposits, as in England, but intercalated throughout the system,-occurring in the Isle of Skye, where they were first detected many