Setting aside the unsatisfactory evidence of foliage and wood, we know, from the remains of fruits of the existence of five species of Araucaria in the Secondary rocks of Britain. One Cretaceous Araucarites Pippingfordensis, Carr., from the Wealden, and the others Oolitic, one undescribed and apparently lost, but determined by Robert Brown, from the Purbeck, one A. Brodiei, Carr., from the Stonesfield slate; and two A. sphærocarpus, Carr., and A. Phillipsii, Carr., from the Inferior Oolite. SEQUOIÏTES GARDNERI, sp. nov., Plate I, Figs. 7, 8. Cone oval, scales peltate, the rhomboidal apex, smooth, depressed in the centre, broader than deep; leaves falcate, incurved, subquandrangular in section, arranged spirally on the branch. Locality. The Gault of Eastware Bay, near Folkestone. For this second British Cretaceous species of Sequoiites I am indebted to J. S. Gardner, Esq., whose researches in the Gault of Folkestone I desire to acknowledge by associating his name with the species. APPENDIX.-The remarkable branches from the Oxford Clay which are represented by Figures 11-13 of Plate II. are placed there with the view of eliciting information regarding them, rather than for the purpose of adding names and descriptions, which mean nothing, to the already long list of uncertain objects that occur in every enumeration of fossil plants. Both forms-that of Figure 11, but especially that represented by Figures 12 and 13-are very remarkable, and easily recognisable. It would specially help to a satisfactory determination of the true nature if either foliage or fruit could be found associated with them. EXPLANATION OF PLATES I. AND II.-PLATE I. FIG. 1. Pinites Leckenbyi, Carr. 2. Section of the same through the axis; the scales and the seeds. The section is not continued to the base of the cone, the lower and lighter coloured portion being fractured. 3. A scale with two seeds at the base. 4. A portion of the base of the cone seen from below, and exhibiting the remains 5. Section of one of the seeds considerably magnified, showing the embryo, in Richard. 7. Cone of Sequoiites Gardneri, Carr. 8. Fragment of a branch of the same. 9. Cone of Pinites gracilis, Carr. PLATE II. FIG. 1. Cast of the fragment of a cone of Araucarites Brodiei, Carr., with a portion of the supporting branch. 2, 3, and 4. Scales of the same; the latter two exhibiting the double nature of the apex. 5. The cast of a fragment of a branch, and 6. A leaf, probably, belonging to the same species. 7. Rolled fragment of Araucarites Phillipsii, Carr., showing the single seed in each scale. 8 and 9. Scales of the same species. 10. Cone of Pinites depressus, Carr. 11. Branch from the Oxford Clay of Chippenham, Cambridgeshire. 12 and 13. Branches from the Oxford Clay of Christian Malford, Wiltshire. 12 from the collection of Wm. Cunnington, Esq., F.G.S.; 13 from the British Museum. II. SUGGESTIONS AS TO GEOLOGICAL TIME. By J. CLIFTON WARD, F.G.S., of the Geological Survey of England and Wales. UT a few years since geologists were in the habit of drawing largely from the Bank of time, and the more they drew the greater was the supply they seemed to want, till at last the thought seemed to come quite natural to them that the supply indeed was inexhaustible. Quite lately, however, these time-speculators have had it suggested to them that there is a limit to the supply, and that the countless ages on which they have depended seem to be very probably but some one hundred millions of years, and untold ages to be reckoned by telling numerals. Just as, however, it would be doubtless a fault in geologists to look up to mathematicians as infallible in the results at which they arrive regarding geological phenomena, so is it unwise to accept for granted the explanation of like phenomena from a cosmical point of view without first putting it to every possible geological test. Now Mr. Croll has very clearly shown that 240,000 years ago our earth was so situated as regards the eccentricity of its orbit, and the position of its northern hemisphere during the summer and winter solstices, as gradually to bring on a glacial climate, lasting until some 80,000 years ago, though having two or more warm periods included within this term of 160,000 years. Can any geological facts be brought forward to test this theory? Now it seems to me that there are but two classes of facts which can be of use in such an investigation, viz. :— 1st. The building up, or wearing away and deposition, of solid material. 2nd. The rising, or falling, of the earth's crust. Under the first class of facts-1st. Building up. Suppose a Coralreef 1000 feet in thickness to be formed on a spot where the refrigerating effects of the glacial climate must have prevented the existence of reef-builders during that epoch, and that such reef presents every appearance of continuity of growth; then, provided we can form an estimate of the average growth of such a reef under favourable conditions, the least time required may be calculated: for instance, taking one foot per century as the rate of increase in vertical height, a reef 1000 feet in thickness would take at the least 100,000 years in forming, and we should conclude that the Glacial period must have ended not less than 100,000 years ago. 2nd. Wearing away and deposition.-Sand and clay to a thickness of some 60 feet is found lying upon Glacial Drift, or surrounding and partly overlapping mounds of such drift, as, for example, in the neighbourhood of York. In the artificial process of warping, each tide not unfrequently deposits about 1-12th of an inch of fresh soil. If comparisons could be made between the natural and artificial methods of warping, the difference in area being allowed for in the two cases, some sort of conclusion might be arrived at as to the length of time that the materials for 60 feet of warp took in being denuded from one spot and deposited in another, such a period being the least which could have elapsed since the deposition of the Glacial Drift. Under the second class of facts, which is, perhaps, less reliable, we may reason thus: - 1st. Elevation.-All observations tend to show that the elevation or depression of the earth's surface takes place very gradually, and extends with tolerable constancy over long periods (this the thick coral-reefs of the Pacific seems to prove); supposing we are able to conclude generally that this movement averages one foot per century over many parts of the earth, then marine Glacial deposits now 1000 feet above the sea would show that they were formed not less than 100,000 years ago.1 2nd. Subsidence.-The case of the Coral-reef in "building up" may also be taken as an example of subsidence within a given period. Now taking some actual examples let us see whether they, even roughly, lend any support to the results arrived at by Mr. Croll. The Peninsula of Florida is made up of some ten coral-reefs one within the other. The whole Peninsula, being only 16 or 17 feet above the sea-level, is formed of the same species of coral, that species being still at work in forming the outermost reef, between which and the Island of Cuba the Gulf Stream flows. Professor Huxley, calling each reef 70 feet thick, and taking the upward growth as one foot per century, has estimated the period for the growth of one reef as 7000, and for the whole Peninsula as 70,000 years, supposing the conditions necessary for a constant increase in height of the reef to be favourable. Dr. Dana, in his excellent Manual, divides the Post-Tertiary Period into the following Epochs: -Glacial Epoch, Champlain Epoch, Terrace Epoch. The Glacial Epoch includes the true Glacial Drift, a deposit due to a vast spread of land-ice reaching down to the latitude of 39°, the epoch being one, Dr. Dana considers, of high latitude clevation. A partial subsidence of the country brought in the Champlain Epoch, softening the climate, melting the vast ice-sheet, swelling the rivers, and causing great thicknesses of fresh-water deposits to be formed along their course and around the large lakes. The shells in these deposits indicate a temperature very similar to the present. During the Terrace Epoch the land was again gently elevated, the elevation being greater in high latitudes-as much as 1000 feet in the extreme north-and lessening southwards, where probably the upward movement was completely lost; then it was that the Champlain deposits were carved into terraces, and sea beaches left high and dry. But to return to the Glacial Epoch: if North America was clad with one universal sheet of ice down to the parallel of 39°, it would certainly have been impossible for coral-animals to have been reef-building 1 Example-The marine shells at an elevation of 1400 feet at Moel Tryfaen, near Bangor; for even if the hypothesis of a 600 feet fall in the sea-level be true, the land must have been raised 800 feet, giving a period of 80,000 years at the rate of one foot per century. only 9° farther south. From this one would argue either that the reefbuilders of Florida began their work before the Glacial Epoch, left it off as the climate became cold, and resumed it at the close of that period, or that the whole structure was of Post-glacial age. If the former was the case, it would seem probable that there might be some indication of it, either in a change of species, or in some more or less marked break in the structure of the Peninsula. I believe there is no such indication; therefore the evidence would lead one to conclude the whole structure to be Post-glacial, and we have already seen that probably the work cannot have taken less than 70,000 years. But if the cold of the Glacial Epoch could arrest the labour of the reef-builders at this particular part, it probably had a similar effect upon other parts likewise. The sheet of ice upon Greenland is acknowledged to have a great effect in cooling our climate at the present time; its removal would have, as Mr. Croll says,' quite a "magical effect upon the entire northern hemisphere:" imagine, then, the power that a sheet of ice occupying the greater part of the northern hemisphere would have in cooling those portions of the globe immediately south of it. There is, however, another point to be considered, viz., that according to Mr. Croll's theory the causes which would in the northern hemisphere produce an extremely cold climate, would in the southern produce a proportionally hot one; the hot southern hemisphere, however, would have its climate more influenced by the cold of the northern, than the northern would have its cold climate affected by the heat of the southern ;therefore the heat would have to retreat as it were before the cold, and the probability is that instead of the hottest part of our globe being situated around the equator, it would lie considerably south of it. In this way the two isotherms of 68°, which are the limits of reef-builders at the present day, would be carried considerably south of their present position, and Coral-reefs would then probably only be in process of formation south of the equator. But do not Coralislands in mid-ocean, with deep water all around, indicate a continuity of upward growth? For suppose an island in the Pacific north of the equator, rising 1000 feet above the sea, to be encircled by a reef; if the land sink at the same rate as the corals can build, say one foot per century, the reef will grow upwards, the island lessening in diameter. But now suppose a Glacial climate in the northern hemisphere to come on and seriously to affect the reefbuilders, they must of necessity die off, migration being impossible by reason of the deep surrounding sea. The subsidence of the land, however, would probably continue, and when the cold was over and the reef-builders might have found it possible to continue their work, there would be no means for them to gain the shores, and the island would go down without leaving an atoll behind as tombstone to mark the spot of its watery grave. Supposing, then, the Glacial climate had a marked effect upon the reef-builders north of the equator, it would be impossible for any of the reefs we now see in that region, surrounding or taking 1 Article in Philosophical Magazine for November, 1868. the place of oceanic islands, to have been commenced before the Glacial Epoch. Let the accompanying woodcut represent the outline of the great Pacific Continent; the line A B is the sea level soon after the commencement of the Glacial Epoch, say 240,000 years ago; suppose the land to be regularly sinking at the rate of one foot per century, in 160,000 years (the close of the Glacial Epoch) the sea-level would be represented by the line CD, the distance x y being 1600 feet in vertical height. During this interval, however (according to our supposition), the reefs 1, 2, 3 north of the equator would have ceased to grow upwards, while the reefs 4, 5, 6 south of it would have continued their upward growth; after this period of 160,000 years the reef-builders would be able to recommence work north of the equator, and No. 4 reef might gradually extend itself further north (in the direction of the arrow) until the Post-glacial reef No. 7 would commence and finally form with No. 4 one great Ideal representation of Old Pacific Continent, to illustrate the theory of the gradual subsidence of the land and the formation of Coral Reefs. encircling reef; but owing to the great depth of ocean which would now separate G from H no reef-builders could find their way to the island G, which would, although other conditions were favourable, be without a reef of any kind; and in some instances it might be the case that the reef 4 would not be able on account of the deep water to wrap round the north side of the sinking island, and in this way some of the strange forms of reefs may be occasioned. The line E F represents the sea-level as it now is after a lapse of 80,000 years, the distance x'y' representing 800 feet in vertical height. We should thus expect to find in the Coral regions north of the equator some islands without reefs of any kind, others with encircling reefs, or atolls of no very great thickness, and therefore small size. This view is somewhat confirmed by the fact that the atolls of the Pacific "diminish towards the equator and disappear mostly north of it;"* and I believe I am correct in stating that the thickest reefs, so far as can be ascertained with any accuracy, occur mostly south of the equator. Dana estimates the whole subsidence in the Pacific area to be not less than 6000 feet, and adds, "It is probable that this sinking began in the Post-tertiary period." Now, since it seems likely that the general rate of subsidence cannot be much more than a foot per century, in order that the corals may keep pace with it, the sinking of this 6000 feet of land would take 600,000 years, Of course the thicker a reef is the larger will be the area which it includes. If Darwin's chart of Coral-Rocks be referred to, it will there be seen that north of 10° north lat., there are but one or two small atolls, while in the southern hemisphere they extend in mass as far as the parallel of 25°. Dana's Manual of Geology, p. 587. |