Sterry Hunt believes that there is a similarity between the crystalline rocks of North America and those of the British Isles.

Among the crystalline rocks of Donegal he has indicated representatives of Laurentian, Montalban, and Huronian; and the latter, he has recently observed, largely developed in Argyleshire and Perthshire. To the Huronian he also refers. the green schists of Anglesea and Carnarvon, in both of which regions the Orthofelsite or Halleflinta series at the base of the Huronian (the so-called porphyries), and likewise the more ancient gneisses, are well represented.

Professor Heddle says:-" Should the conjecture of Murchison and Geikie, that the gneiss of the west coast is of Laurentian age, prove to be correct (as, indeed, there can be little doubt), and should the Shetland rocks, with equal correctness, be assigned to the Huronian, then in the philite schists of Boharm and Clova, the andalusite schists of Coreen, the staurolitic and andalusite schists of Kinnairdy, the quartzites and limestones of the Vale of Deskford, Ben Cullen, and away to the south, the serpentines, granular hornblendic rocks, chiastolite and margaroditic schists of Portsoy, we have another series equally accordant with the Taconian of

America."

In none of the geological formations in the neighbourhood of Inverness are these Banffshire schists represented. The only thing resembling them is the rock underlying the Old Red Sandstone of Dunchea, which was pointed out in my paper on the "Structural Geology of Strathnairn," as differing from the ordinary Gneiss in appearance.

In the absence, however, of a minute mineralogical examination of the latter, it would be unwise to assert that the underlying rock on Dunchea was a fragment of the eastern schists.

Travelled Boulders.

Having revisited this district at Christmas 1879, and examined it more carefully than on former occasions, I found further proof of the eastern flow of the great ice sheet that at one time covered or traversed the whole of the south shore of the Moray Firth.

In the neighbourhood of the Enzie post-office I found numerous boulders of the so-called Ben Wyves granite. None of them were so large as the one which was dug out during the excavations for the Buckie harbour, and seen on a former occasion.

Numerous small boulders of the Elgin Cornstones lie scattered all over the lower part of the district. Several are to be seen in the Gollachy Burn, a little to the west of Buckie.

Conglomerate boulders are rather rare. Except the few remaining stones forming the "Stone Circle of Dryburn," I found only one, about a quarter of a mile east from Dryburn.

A very characteristic specimen of Kinsteary granite (near Nairn) was dug out during the excavations for the new harbour at Buckie. Smaller pieces may easily be picked up on the fields and along the shore.

A well marked feature of the schists which underlie the Old Red in this district, is the frequent occurrence of large veins of calk spar, quartz, and quartzite.

Specimens of these are also numerous in the drift.

A fine specimen of cairngorm, which was water-worn, was picked up by a labourer on the high ground, locally known as the "Hill of Altmore," to the south of the district.

It measures 2 inches thick at the one end and 3 at the other. It is about 4 inches in breadth. This man, ignorant of its value, took it to Aberdeen, and had it polished on both sides by some friend at the granite works. This has rendered it quite transparent, so that one can read with the greatest ease any book placed under it.

As far as the boulder evidence goes, it proves conclusively, I think, that the ice-flow was from the west, or a little to the south of west.

One section of boulder clay is deserving of notice. It is in the wood of Pathhead, on the estate of Cairnfield, and a little to the south of the Enzie post-office.

It consists of a fine plastic clay, of a dark bluish-black colour, overlaid by the well-known red boulder clay.

The blue clay would point to the denudation of the schists, and the red to that of the Old Red Sandstone.

Notwithstanding a very minute examination of every burn in the district, I failed to find any of the blue clay on the lower ground.

This I take to be an additional proof of the easterly flow of the ice.

All along the south shore of the Moray Firth, lie scattered boulders of sandstones and Conglomerates, Dirriemore, and other granites, and the sandstones and cornstones of Elgin.

In the neighbourhood of Inverness these would indicate a drift from the N.N.W., and tending E. or a little to the N. of E. Boulders of hornblende, which can also be picked up, might come from the N.W. The only places where I have seen hornblende in situ, in the neighbourhood of Inverness, are at Raven's Rock, near Strathpeffer, and on the north shore of Loch Ness.

IX.-Notes on Ulodendron and Halonia.* By D'ARCY W. THOMPSON, Edinburgh. (Plates.)

(Read 20th May 1880.)

The anomalous and singular appearance of the scars upon the bark of Ulodendron, and the fact that no organ or appendage has ever been described in definite relation to them, sufficiently accounts for the extreme diversity of the opinions which have been held regarding their nature and mode of formation.

Leaving out of consideration such old, forgotten theories as that of Rhode's, who, long ago, looked upon them as the remains of crushed and disfigured flowers, more recent authors have at different times considered them to be points of attachment for leaves or cones or branches, or even for aerial roots. A careful summary of the results of previous writers will be found in a paper on this subject by Mr Carruthers, which was published in the "Monthly Microscopical Journal" for March 1870; and it will accordingly be unnecessary for me to recapitulate here the opinions which were therein criticised. Mr Carruthers himself came to the conclusion that the scars of Ulodendron gave origin to aërial roots, and he did so for the following reasons:-Firstly, he said that whatever organ it was that sprang from the scar, it was attached to the scar's whole surface, and Mr Carruthers gave a diagram of the various tissues passing out of the stem, and declared that a branch or an aërial root would alone fulfil the conditions of arising from so large a surface. Secondly, in a specimen which he described under the name of U. tumidum, the scars were elevated upon raised protuberances, and the surface of each scar was here shown by Mr Carruthers to have a slight downward inclination. The organ which sprang from it could therefore be no branch, and accordingly he concluded we must think of it as an aërial root.

In Professor W. C. Williamson's papers in the "Transactions of the Royal Society" on "The Organisation of the Fossil Plants of the Coal-measures," a brief space only is devoted to the two genera Ulodendron and Halonia; but for all that, the short account given of them is a most valuable item in our knowledge of the plants. After referring to a specimen of Ulodendron, in which the scar was seen to occupy the summit of a considerable elevation, corresponding exactly to one of the tubercles in a decorticated Halonia, the Professor proceeds to describe the vascular bundles which, in Halonia, pass out to these tubercles; and after comparing their arrangement with the * These notes were for the most part written in the winter of 1878-79, but from various causes their publication has been delayed.

ordinary phenomena of branching in Lepidodendroid plants, he infers that these bundles "proceeded to some modification of a branch, but which modification was of smaller dimensions than branches usually attained to, and which, consequently, required a less abundant supply of vascular tissue than ordinary branches needed. Such modification would only be found in a strobilus, which must be regarded as a branch that has undergone an arrested development at a very early stage of its growth." The Professor concludes in the following terms:-"Every new fact that we discover seems to me to bring the two genera, Halonia and Ulodendron, into nearer relationship than has been hitherto recognised. I have very little doubt that the Halonia were young branches, sustaining rows of cones. After the cones fall off, they would leave permanent cicatricula impressed upon the bark, and which would enlarge as the stems increased in magnitude, the latter process being probably accompanied by the development of an exogenous zone around the medullary cylinder. Specimens of these old and matured fruiting stems may exist among what we have hitherto termed Ulodendron. This explanation would give us the reason why we never find cones or other appendages of a magnitude corresponding with the cicatricula of Ulodendron."

Professor Schimper, in his Traité de Paléontologie Végétale, though, like previous authors, he had seen no specimen of Ulodendron with any organ attached to the scar, deduces from the form and markings of the scars the following theory, which corresponds very closely indeed with that which I shall endeavour to prove from the specimens presently to be described. He considers the large scars to indicate the points of attachment of cones, which seem to him "Avoir persisté assez longtemps et au moins jusqu'au moment, où, à la suite de l'épaisissement du sympodium, leur point d'insertion a été débordé par l'écorce de ce dernier. Celui-ci se trouve, en effet, refoulé dans l'épaisseur de l'écorce, où il occupe le fond d'un creux. Ce creux lui-même, s'est probablement moulé sur la base du cône, qui, de cette manière, a pu y laisser l'empreinte de ses bractées inférieures, ou des feuilles du petit rameau qui le portait."

Principal Dawson, in his "Acadian Geology," also inclines to the belief that the scars of Ulodendron were produced by the impressions of large cones, and he associates the genus with certain other forms, under the new generic name of Lepidophloios.

Ulodendron is, on the whole, a common and characteristic fossil in the bituminous oil-shales of the neighbourhood of Edinburgh, and during the last two years I have lost no opportunity of obtaining specimens of the genus, along with other coal-plants from the pits around that city, and the following notes are the outcome of an examination of a large series of such specimens:

The Scars of Ulodendron.

The scars of Ulodendron are, as is well known, arranged in two longitudinal rows upon the branches, one on either side, and the scars in one row alternate with those in the opposite one. They are placed at regular intervals, though the intervening distance varies greatly in different specimens, for they are occasionally so close as to be almost contiguous, and are sometimes separated by a space of many inches. In size also they are subject to great variation. The smallest branch which I have seen, measuring about 14 inch in diameter, exhibits scars whose diameter scarcely exceeds half an inch, while the scars upon larger specimens of the same species often attain a diameter of more than 2 inches. U. commutatum, according to Schimper, occasionally possesses scars nearly 8 inches long.

In shape, the scars vary from a circular to an oval or elliptical form, and, indeed, they exhibit as great a range of variation in this character as in size. The round scars are seldom to be seen of large size, rarely attaining a diameter of more than 1 inch or 1 inch, and they are certainly, as a rule, the best preserved, and show their characteristic markings to the most advantage. The oval specimens owe their shape, I believe, exclusively to secondary causes; for no organ which we can conceive to have been attached to the scars of Ulodendron could have left by its direct impression a cicatrix of such a form. But pressure, oblique or lateral, during the process of fossilisation, will, to a great extent, account for this; and this explanation seems to me all the more likely, since we find corresponding distortions of the leaf-markings, and long cracks in the bark, &c., occurring in connection, almost universally, with the oval scars. Besides this means of producing the effect in question, there is another of very great importance, and whose bearing on the present case was originally suggested to me by Professor Williamson. I allude to the subsequent growth of the tree. For, as I have already mentioned, the oval scars are usually of comparatively large size, and indistinctly marked, and we may accordingly suppose that the appendicular organ having fallen off, the rapid vertical growth of the tree would lead to a corresponding elongation of the longitudinal axis of the scar. We do not by any means always find the long axis of the scar coinciding exactly with that of the branch, for it is often more or less obliquely situated, and the shape is not always a true and regular oval, but is often greatly distorted in various directions. We never, to my knowledge, see scars of Ulodendron whose breadth is in excess of their length-a condition which we might expect to find if there had at any period been great radial growth.

I have said above that the oval scars are generally rather

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