The genus Brachymetopus was founded by McCoy in 1847, and the generic characters were drawn from the Australian species Br. Strzeleckii, McCoy, which was at the same time described. The specific characters of this form were very briefly given, the leading features having been mentioned in the diagnosis of the genus. Dr. Henry Woodward in 1884 gave a new summary of the generic characters differing somewhat from that originally furnished by McCoy, being modified in such a way as to include the European or British species, Br. ouralicus, De Vern., Br. Maccoyi, Portl., Br. discors, McCoy, and Br. hibernicus, Woodw. The original type-specimens of Br. Strzeleckii used by McCoy (op. cit.) in drawing up the description of the genus, and figured by him at the same time, are in the Woodwardian Museum, to which they were presented in the year 1844 by the Rev. W. B. Clarke. They come from the Carboniferous Shale of Dunvegan, New South Wales. The specimens comprise three complete head-shields, two of which are hollow impressions and one a cast, and portions of three or four others; there are also three casts of complete pygidia, one perfect impression, and fragments of two others. This material demands a fuller description of the specific characters than McCoy furnished, particularly as this type-form of Brachymetopus shows features differing in several respects from those of the better known European species ascribed to the same genus. McCoy's description (op. cit.) of the species was as follows:—

“Glabella widest at the base, with one very minute, obscurely marked, cephalothoracic furrow at the base on each side; all the segments of the pygidium with an irregularly tuberculated ridge along the middle; lateral segments forming large tubercles where they join the thickened limb, opposite each of which is a short slender spine projecting from the margin”.

Varieties of the Creechbarrow Limestone.—There are considerable extremes in this respect, ranging from a soft marly deposit, which soils the fingers like whitening, to a hard compact rock, which takes a good polish. Unquestionably the most dense and compact lime-stone is that near the summit, whilst the soft marly beds are on the northern slope, and especially near the 500 feet contour, where some of them are earthy and contain a considerable amount of impurity, so that they may at least be called marly limestones. On the other hand, there are compact white limestones, where nests of dog-tooth spar form no inconsiderable portion of the mass. Quartz grains may be noted on most of the weathered surfaces.

The more compact and denser limestones, which prevail near the summit, may be roughly divided into non-pisolitic and pisolitic rocks. Thus, for instance, I have before me (Group 1) specimens of a very heavy and partially calcitic rock. It is a hard whitish limestone without pisolites, but largely interspersed with buff-coloured patches, not unlike some dolomites. Calcitic nests and strings occur, and also strings and stars of black oxide of manganese: the external surface is rough and somewhat honeycombed, and full of curious impressions, some of which may have had an organic origin.

Group 2 comprises those specimens where the pisolitic character is indicated, but not very obviously. A characteristic specimen may be described as follows:—A large fragment of a creamy white tufaceous limestone, with specks and threads of black oxide of manganese in places: flattened pisolitic bodies in brownish calcite are numerous, but not very distinct.

From time immemorial a remarkable accumulation of bones in the province of Teruel, Spain, has attracted attention. It is especially conspicuous in the low range of hills near Concud, and the people of that village seem to have generally regarded it as marking an ancient battlefield. So long ago as 1754 Torrubia briefly described this deposit in his Spanish Natural History; but his curiosity seems to have been aroused not so much by the bones themselves as by the crystalline calcite found occupying many of their cavities. Twenty years later an Englishman, William Bowles, again referred to the same bone-bed, and described it as containing the remains of men and women mingled with the bones of horses, donkeys, oxen, and smaller domestic animals. He also observed that the limestone above the bone-bed was filled with land and fresh-water shells. Cuvier quoted Bowles' description in his treatise on fossil bones, and after an examination of some teeth and bone-fragments collected by Proust at Concud, he was inclined to believe that these fossils really represented domestic animals as already determined, though he found no associated evidence of man.

About a year ago my friend Professor Dobbie, of the University College of North Wales, drew my attention to the remarkable experiments of Sir W. Roberts-Austen (whose premature death we must lament as a very great loss to science) on the diffusion of solid metals, suggesting that they might have some geological application. The phenomena referred to in this paper, in which I have been very keenly interested ever since my work as a Geological Surveyor in Eastern Sutherland, occurred to my mind at the time as a probable case; but after some reflection certain difficulties began to appear, and I put the subject aside for a while. The very suggestive address of General McMahon to the Geological Section of the British Association at Belfast has reawakened my interest; and it seems to me worth while to put forward some considerations on the matter, somewhat speculative indeed, but which may perhaps be of service in stimulating research on a fascinating though difficult subject.

Some time ago my friend Mr. Jukes-Browne asked me to examine some sand, with a view to ascertaining whether it was derived from Dartmoor. Dartmoor quartzes have so many specific characters that it is often easy to say that a quartz is not derived from that region; but owing to the fact that quartz-veins have not been studied, it is usually impossible to say whence various sands have in fact come.

A proper interpretation of some geological phenomena requires that allowance shall be made for differential earth-movements that have taken place since the period of occurrence of the events or conditions under consideration.

Present differences of level in rocks of the same age may be partly due to actual differences in depth of the sea-floor on which they were deposited, but they may also be the results of subsequent differential earth-movements either of a regional or of a local character, the latter including ‘fauhs.’

In order to estimate the amount of displacement or differential movement, it is necessary to select a particular rock as a datum. The rock selected should combine, as far as possible, the following characteristics:—

1. It should be comparatively thin.

2. It should have a considerable horizontal extension.

3. It should combine similarity in physical characters and palæontological contents over a large area, so that uniformity of depth of deposit may be postulated.