This widely-spread, and, on the whole, well-marked species, has been in so many cases, as it appears to me, confounded with Alaria bispinosa, that it would be a task of no small difficulty to trace out the mistakes that have arisen in consequence. The imperfect figures of Phillips have, no doubt, been the principal cause of thus confounding the two species. Deslongchamps queried the identification, but yet was inclined to adopt it. Morris and Lycett seem to have had no doubt on the subject. “Having had the advantage of examining a large number of specimens, comprising every variety both in form and stage of growth, we feel no hesitation in uniting the two species here indicated.” It is extremely probable that the Great Oolite specimens of Alaria trifida present varietal differences from the Oxfordian types, and they may also in some cases have assumed forms having only one lateral digitation; but higher up in the Jurassic rocks they seem to be very fairly separable for such a genus as Alaria, which is so prone to effect changes in its shell. Such was doubtless the opinion of Morris, who quotes Al. bispinosa from the Lower Calc. Grit and Kel. Rock, whilst Al. trifida is quoted as a distinct species from the Oxford Clay and Kel. Rock of Yorkshire, the Great Oolite form being referred to a variety.

The following propositions respecting faults apply to strata, which are either horizontal, or which have a uniform dip. If they have a uniform dip, the country, faults and all, may be supposed turned back through the angle of dip, and the strata will become again horizontal. We need then only think of horizontal strata, if we bear in mind that “horizontal” and “vertical” really mean only, parallel and perpendicular to the bedding. This artifice will simplify the subject; but it does not imply that the faulting took place before the beds were tilted, which may, or may not, have been the case.

Recently, while reading Dr. Davidson's description of his Eichwaldia Capewelli, Brit. Sil. Brach. Sup. pp. 140–1, I was much interested with that paragraph in which he states, “It had been suggested to me that the appearance of the sculpture of the surface of E. Capewelli is precisely that of certain Polyzoa one is accustomed to meet with in Palæozoic rocks, a fact that had struck Mr. R. Etheridge, jun., as well as Prof. Nicholson; but to accept the ornamentation as that of an encrusting Polyzoan we must suppose that the shell had been entirely replaced by the parasite, as sometimes occurs with Hydractinia. Sections, however, show a perfectly homogeneous structure of the whole thickness of the shell.”

On no branch of geology has there been more imaginative writing than upon metamorphism. Some speculations have, indeed diverged into the humorous. Keen-eyed observers, with vision capable of piercing through miles of solid rock, have described to us those processes of subterranean cookery by which Pluto has converted sandstones and shales into granite, metamorphic schists and porphyries. If water was used, the rocks were “stewed”; if not they were only “baked” or perhaps “melted.” Furthermore, it was declared, and text-books submissively taught, that rocks of almost every epoch have sometimes undergone these mystic changes: In North America, some metamorphic schists were “Triassic” while in the European Alps we had granite and gneiss of “Eocene” age. In Britain, men were more moderate, and we were not asked to extend our faith beyond the limits of the Palæozoic formations. The evidence on which these conclusions were advanced was mainly of two kinds. A metamorphic rock associated with unaltered beds was proved to be of the same age as the latter, because either it overlay or passed into them. Thus, as an illustration of the former, the newer gneissic rocks of the Northern Highlands were said to be Ordovician, because they rested on Ordovician limestone and quartzite. Murchison saw the gneiss lying on the top of the limestone or the quartzite, and he said that the upper beds were the younger. Everybody believed him, except Nicol, who died discredited and disheartened. Now, we know that Nicol was right, and the great authority, misled by superficial appearances, was wrong.

The German Expedition to South Georgia has brought back the interesting information that this island, situated in the Antarctic Ocean, Lat. 54° S., Long. 37° W., is composed of clay-slate. Not only the part the members of the expedition were able to inspect was found to be composed of this slate-rock, but the glaciers brought down the same rock from the central portion of the island. In some places the slate was interspersed with varieties of quartz. No metals were found, but the rock contained a little iron, a quantity insufficient to affect the magnetic needle.