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microscopical sections of M. crassa have entirely confirmed Mr. Rofe's discovery of this reticulated tissue, but have failed to demonstrate its existence elsewhere than in the substance of the walls of the corallites. So far as our observations go, we find the visceral chamber of the corallites of M. crassa to be entirely open and free from tabulæ, being usually filled with matrix from end to end (Fig. 2e). This being the case, M. crassa clearly conforms to the definition of the Zoantharia tubulosa laid down by MilneEdwards and Haime, and cannot be regarded as a member of the old group of the "Tabulata." In this respect, also, it differs from C. Michelini, as well as from those examples of Aulopora, which we have been able to examine by means of thin sections. Moreover, its structure is quite peculiar, and so far as we know, such as does not occur in any known coral except the present. The wall (Fig. 2e) is extremely thick, and for the most part exhibits a distinctly fibrillated structure, as if composed of successive concentric layers, this structure being equally conspicuous in longitudinal and transverse sections. In parts of the corallum, however, the concentric lamella of the wall become separated from one another so as to include a series of distinct interspaces or cavities, which are approximately parallel to the axis of the visceral chamber, and which are crossed at right angles by numerous delicate cross-bars or trabeculæ of sclerenchyma (Fig. 2, e and f). This singular reticulate or cellular tissue seems to be sometimes partially developed in the basal portions of the corallum (see Fig. 2, d), but is essentially and principally, if not altogether, present in that portion of the wall which forms the actual cup of each corallite. As before said, we have entirely failed to discover any traces of this cellular tissue as encroaching upon the true visceral chamber; and there thus arises a discrepancy between our observations and those made by Mr. Rofe (loc. cit.). This, however, may admit of explanation if we suppose that the longitudinal section figured by Mr. Rofe has really been excentric, and that instead of passing along the axis of the visceral chamber, it has really traversed the thickness of the wall. We are at present unable to parallel the peculiar structure of C. crassus, as above described, with that of any other coral known to us, nor can we offer any opinion as to the precise functions or homologies of the cellular tissue of the calicine walls.

Loc. and Horizon.-Carboniferous Limestone of Derbyshire and Lancashire; Gilbertson and Rofe Collections, British Museum.

So far, therefore, as our preliminary examination of certain species of Cladochonus has gone, it would appear that the genus as originally constituted contained corals of very different structure, judging by the conformation of C. Michelini, and C. crassus. The latter has a special structure of its own, quite distinct from C. Michelini, as well as from Aulopora, and for it we have ventured to propose the generic name Monilopora.

In conclusion, we have to express our thanks to Professor Geikie, F.R.S., for the use of specimens contained in the Collection of the Geological Survey of Scotland.

EXPLANATION OF PLATE VII.

FIG 1.-a. Two examples of Cladochonus (Aulopora ?) Michelini, E. and H., of the natural size, Lower Carboniferous, Dunbar.

b. A small example of the same enlarged five times.

c. A longitudinal section supposed to be of the same species, enlarged five times. d. Portion of a colony of Aulopora sp., from the Devonian of Ontario, of the natural size.

e. Longitudinal section of part of the same, enlarged five times.

f. Cross-section of a corallite of the same, similarly enlarged, showing the tabulæ. g. Portion of a colony of Aulopora repens, E and H., from the Eifel, of the nat. size. h. Section of the same, enlarged seven times, showing curved tabulæ.

FIG. 2.-a. A full-grown colony of Monilopora crassa, M'Coy, growing upon the stem of a crinoid, of the natural size.

b. A younger colony of the same, encircling a crinoidal column, and viewed from above, of the natural size.

c. A detached fragment of the corallum of the same, of the natural size. d. Transverse section of a young colony of the same growing upon a crinoidal column, magnified 2 diameters (the visceral cavities of the corallites are more or less largely filled with matrix, and the peculiar reticulated structure of the skeleton is here and there visible in the wall, while the whole has been finally enveloped by the growth of the stem of the crinoid).

e. Longitudinal section of a single corallite of the same, enlarged five diameters, showing the open visceral chamber, the fibrous wall, and the reticulated structure of the wall of the calice.

f. A portion of the reticulated tissue still further enlarged.

All the specimens are from the Carboniferous Limestone of Lancashire. (British Museum.)

II. HOW THE APPEARANCE

OF A FAULT MAY BE PRODUCED WITHOUT FRACTURE.

By W. O. CROSBY, S.B.

HE general structure and mode of growth of coral reefs and

stance of considerable geological interest, to which, so far as I am aware, attention has never been called. This is the peculiar stratigraphic relation of the different strata in the reef to their chronological equivalents in the deposits of the surrounding ocean; a relation due to the comparatively rapid growth of the reef as a whole.

Deposits of some sort, it may be safely said, are forming in all parts of the sea, of coarse materials and with comparative rapidity in shallow portions adjacent to the land, and of finer sediments and with extreme slowness in the oceanic abysses remote from the continental borders. Calcareous sediments usually accumulate much more slowly than those of mechanical origin, but to this statement the limestones of coral reefs probably constitute an important exception; while the growth of the reef under favourable circumstances is incomparably more rapid than the vertical increase of the impalpably fine, and mainly organic, ooze and mud covering the greater part of the ocean floor. This is proved by the fact that the coral reef and island are usually able to keep pace during countless ages with the progressive subsidence of the sea-bottom, so that their living growing crests are always within reach of the sunlight and air, while the dead and consolidated mass below stands like a wall towering thousands of feet above the slowly increasing and yet strictly synchronous deposits of the surrounding ocean, which appear to maintain their fineness and uniformity up to the very base of the reef.

The numerous soundings made in the vicinity of reefs have shown that their outer slopes are usually very steep and abrupt, often nearly vertical, and in some cases probably overhanging. Although undoubtedly extremely ragged and cavernous, at all depths below one hundred, or at the most two hundred, feet, these slopes are beyond the influence of the waves; and in consequence are not subject to decay, except as the calcareous matter may be slowly attacked by the carbon dioxide so abundant in sea-water at great depths.

Of course when the formation of a reef first begins, it is on the same level with the differently and more slowly formed but synchronous sediments of the adjacent portions of the ocean-bed; as its growth continues, however, it rises wall-like above these, and synchronous layers in the two sorts of deposits, always differing in thickness, are no longer stratigraphically continuous, those in the reef lying at higher levels than those outside. And with the lapse of time the vertical separation of beds of the same age must become greater and greater; so that if we may assume that the reef grows three feet (a low estimate) while the surrounding deposit is rising one foot, then when the former has attained a height of three thousand feet, the latter will be only one thousand feet thick, and the last-formed beds on either side will be separated vertically by two thousand feet. Supposing now that the subsidence, and, as a necessary consequence, the growth of the reef cease, then the gradual silting up of the outside ocean will continue as before, and in the course of time we will have, theoretically at least, lying on the same level with the upper part of the reef formations of a much later age, as shown in the diagram, where the horizontal bands within and without the reef are to be synchronized according to the numbers.

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The reef is elevated to form dry land, and subsequent erosion developes the surface a b. Thus there is produced the general appearance of a fault, but without a fracture; and it is easy to conceive how a geologist might be deceived and led to conclude that the old coralline limestone of the reef had reached its present stratigraphic position through the agency of a fault.

In this pseudo-fault, it will be observed, the vertical displacement gradually diminishes downwards, becoming zero at the bottom of the reef; and many true faults, geologists are agreed, must die out below the surface in a manner equally gradual. Of course observation of

the actual contact would probably undeceive the careful student, as the merely seeming fault would bear little resemblance, on close examination, to a bona fide fracture; but it is necessary to remember that our knowledge of the existence of faults usually rests upon more or less probable inference rather than direct observation.

Many coralline limestone formations are regarded by geologists as ancient reefs, and other limestones more compact may very well have had this origin, for it is well known that on modern reefs much of the rock formed only yesterday, as it were, is exceedingly compact and almost destitute of recognizable organic remains. My knowledge of the stratigraphy of our old reef limestones is too imperfect to enable me to determine whether their relation to the bordering formations is often such as I have sketched above, but it seems very improbable that this relation should not exist in some cases.

III. THE SLOW SECULAR RISE OR FALL OF CONTINENTAL MASSES. By KARL PETTERSEN, Tromso.

JOIN

[OINING a foreign geologist, who was staying here a while last summer on his journey to the North, I followed the old shoreline or sea-level of Bredviken, cut in the solid rock, and extending along the north part of the island of Tromso, near the sound bearing the same name. When, at the end of that line, about Oerendalen, we threw a glance at the low ground beneath, named Skatoeren, this appeared furrowed with a series of natural ditches, stretched horizontally and parallel to the present coast. Seen from above, they were marked very sharply and distinctly. This attracted my attention, the more so as I had often been there, and as frequently traversed the plain, without having discovered the fact. We accordingly went down on the low ground to examine the matter more closely, but it did not appear there so distinctly, as might be supposed when seen from above. But after a more searching examination, we succeeded in detecting a series of more or less distinct and parallel furrows. Our time being limited, however, we could make no closer inquiry for the moment; but as I considered the matter worth more minute studying, I returned to the place a few days afterwards.

I did not see furrows this time from above as distinctly as last, owing to a less favourable light, and on the plain itself I now found it very difficult to trace every single furrow. The only way to do so was to fix your eye from above upon a single furrow, then walk down to it, and follow its course across the plain.

The flat low ground at Skatoeren is, it seems, composed altogether of remains of shells, mixed with sand. It ascends gradually from the present shore for nearly 120 mètres up to a height of about 10 mètres, thus forming the base of a row of hills that rise from its upper side. The plain has, it is evident, extended a great Ideal farther north. In course of time great washings and slips have taken place in that direction, and thus the plain in our day ends in a steep bank, consisting completely of shell-sand. The subsoil of the lowland, which consists of shells and sand, is over

grown on the surface with moss, which mossy cover is intersected crosswise with furrows, caused by the water purling down from above. At the first glance the surface appears as an infinite number of molehills, cut separately, and spread irregularly all over the plain. By this constant digging out, the original furrows, notwithstanding their distinct and regular course, when seen from above, have been effaced to the view so much, that you have some difficulty in discerning most of them when you walk across the plain. From the sea upwards you will meet, at first, four successive furrows, at a distance from one another of about 3 mètres. From the fourth one there is an interval of 13 mètres to the next, that has been traced. This furrow is very distinct, and may be pursued longitudinally for 70 mètres. Above this one I have found still eight more furrows at different intervals, the highest of which lies about 8 mètres above the surface of the sea. It is very probable, however, that there are many furrows besides the above mentioned that have not yet been traced, or have perhaps been effaced.

When seen from above at least, the furrows appeared, however, close to each other, and seemed to follow each other at more regular distances.

There can be no doubt, it seems, that these furrows have been formed by the surf. Where our shores are made of fine sand or crushed shells, you will frequently find one or even several successive ridges, like walls, running parallel to the beach, caused by the lashing of the waves, that heap the sand in long drifts, lying in one level.

The uppermost of those lines on our present coast generally indicates the highest spring tide.

When seen from above, there is a striking likeness between the before-mentioned furrows and the ridges on the present beach.

With regard to our Arctic regions, it has already been proved some time ago, that the rise of the land, for the last 10 to 12 mètres at least, must have been effected slowly and evenly. Those proofs may be found in the frequently appearing banks of shell, that rise, in some places without interruption, from the present shore up to a height of about 10 mètres.

What we have said about the furrows at Skatoeren seems to prove, still more decidedly, that the rise has gone on by degrees and uniformly. Such perfect preservation of a series of successive shore-lines or margins admits of no supposition of a violent or sudden change of level.

John

As to the question of the secular rise or fall of the continent, relatively to the level of the sea, it has been considered long ago a scientific fact amongst most geologists, that during this change the surface of the sea has been, on the whole, unchangeable. Playfair was, it is well known, the first who held this in his "Illustrations of the Huttonian Theory," published 1802. In that work he even mentions the slow rise of Sweden. Quite independent of that book, Leopold v. Buch comes to the same result. In his publication of 1810, "Journey through Norway and Lapland," he accentuates the

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