Before proceeding to describe the more common porphyrites, I wish to return to the subject of the true andesites, referred to in my last paper, and their relation to Tertiary and recent rocks of a similar chemical and mineralogical composition. On referring to the note appended to that paper, it will be seen that my description of the pyroxenic constituents of these rocks was very imperfect, not to say inaccurate. The number of elongated sections which extinguished parallel with the vibration-planes of the crossed Nicols attracted my attention when first I examined the rock, but seeing that the same feature occurred in the so-called augite-andesites of Hungary and Santorin, and seeing further that as regards cleavage and crystalline form the pyroxenic constituents of the Cheviot rock resembled those of the augite-andesites above mentioned, I came to the conclusion that the prevailing pyroxene in both cases was the same, and also that it was augite. In the former conclusion I still think I was right, but in the latter I was unquestionably wrong.

In those parts of Britain upon which all geologists are agreed with respect to the natural order of their ascending series of rock-formations, the stratigraphy is of a comparatively simple character. The beds are either gently inclined, or but slightly convoluted. The rules by which the original sequence of the strata is worked out have been settled by common consent. The nature and effects of those physical accidents which have affected the rocks subsequent to their deposition have long since been almost exhaustively worked out. The rules and conclusions thus developed are now-a-days part and parcel of the working material of every field-geologist worthy of the name.

I have just received from Mr. C. H. Hartmann, of the “Range Nurseries, Toowoomba, Queensland,” a neighbour of my friend Mr. G. F. Bennett, to whom I am indebted for fossil remains from that locality (Megalania, e.g.), an outline of the entire skull of a Thylacoleo. It is a basal view of the skull in which the teeth of the upper jaw are indicated in situ, determinativeof the genus and apparently species. The writer states, “I have only just drawn a pencil outline round the skull soas to give you the right dimensions1—the most remarkable appearance is that there is scarcely any brain, bu very strong and thick bones.”

Griffithides, Portlock, 1883.—Outline oblong oval; glabella pyriform, gibbous in front, destitute of lateral furrows; basal lobes inflated; cervical lobe broad; eyes small, lunate, smooth; axial furrow clearly defined, outline of free cheek broadly triangular, outer posterior angle sometimes produced into a cheek spine. Thorax with nine segments; pygidium rounded, composed of from ten to thirteen coalesced somites.

In previous articles the writer has given the more important characters of the order Sauropoda. A volume on this group is now in preparation, and the illustrations (90 plates) are nearly completed. One of these is a restoration of Brontosaurus, which has so many points of interest that a reduced figure is here presented. Several new characters of this group are added, some of which will be of interest to comparative anatomists.

During some excavations which have lately been carried on by Mr. J. J. Colman, M.P., at Corton Cliff, Suffolk, a number of Mammalian teeth were dug out of the “Forest Bed,” and these specimens, at the suggestion of Mr. James Reeve, of the Norwich Museum, Mr. Colman has very courteously allowed to be sent to me for examination and description.

The theory of the origin of continents and ocean-basins developed during the last third of a century, chiefly by Prof. Dana, and commonly known as Prof. Dana’s theory, is now accepted by many geologists. The main points in this theory, as gathered from the latest expression of Prof. Dana’s views, are the following:1— The earth, superficially at least, is, and was originally, before it had a solid crust, of unlike composition on different sides. This heterogeneity caused a corresponding difference in heat-conductivity. The more rapidly conducting areas cooled fastest and were the first to become covered with a solid crust. Solidification is attended by contraction; and therefore the newly formed crust must have been heavier than the liquid immediately beneath it. As a consequence, it broke up and sank until it reached a liquid stratum of the same specific gravity as itself; and afterwards the process of crusting and sinking went on until a solid crust was built up from this point to the surface. Through the continued escape of heat this primitive crust is thickened, and is still thickening by additions to its lower surface. These first formed portions of the crust became, and will always continue to be, the continents. The remainder of the earth’s surface was still liquid, after the solidification of the continental areas was well advanced; and, of course, as long as it continued liquid, its surface was level with that of the crust-areas. Finally, it became the theatre of a similar process of crusting and sinking, and at last permanently froze over. Now the main point is that the contraction of this inter-continental crust during its formation caused its surface to sink below that of the continents; and the depressions thus developed became the future ocean-basins, which, like the continents, are necessarily of a permanent character. Indeed, it is a plain deduction from Prof. Dana’s theory that the existing continents and oceans are as old as the earth’s crust; and that during the course of geological time the continents have become constantly wider and the oceans deeper.

Some years ago my friend Mr. Robert Damon, F.G.S., of Wey-mouth, visited the Cretaceous deposits of the Lebanon, and when at that place he was so fortunate as to make the acquaintance of the Rev. E. R. Lewis, M.A., F.G.S., Professor in the Syrian Protestant College, Beirût, Syria.

The rarity of specimens of Sigillaria with foliage attached makes the specimen figured on Plate II. of great value. Since Lindley and Hutton figured a fragment of Sigillarian leaf, and from its nervation referred it to Cyperaceœ under the designation of Cyperites bicarinata (plate 43), not a little has been done to elucidate the foliage of this important genus.

The usually quiet city of Prague in Bohemia, with its population of 235,000 inhabitants, considerably more than half of whom are Czechs, has been deeply moved by the recent death of an old French exile, who for more than half a century had made his home there, and, having taken up the geology of the country around Prague for his study, had endeared himself to the people by learning their language and interesting them in his pursuits. After publishing at great cost his geological works, and amassing a vast collection of fossils, he has at his death bequeathed his Library and Collections (valued at £20,000) to the Prague Museum, together with funds for the completion of his scientific labours. “To-day,” writes Dr. Fritsch, “I have opened a ‘Barrande Fund’ with 1,000 florins, which I hope will soon reach to fl. 20,000; its object being to promote the study of the Silurian formations of Bohemia. We also wish to place a large slab inscribed with the name of ‘Barrande’ on the Silurian rocks in Kuchelbad, near the celebrated locality Wiskočilka, where he picked up his first fossil Orthoceras Bohemicum.”

The remains of Birds from Quaternary deposits in this country have been so rarely recorded, that any fresh evidence, throwing light upon our Pleistocene avian fauna, cannot but be of interest. The specimen about to be described was found in the “Mundesley River Bed,” from whence was obtained the Emys lutaria described in this Magazine in 1879 (Dec. II. Vol. VI. p. 304). In a note appended to that paper, Mr. H. B. Woodward has given a short account of this Mundesley deposit, and it will be found fully described in the Geological Survey Memoir, by Mr. C. Reid, “On the Geology of the Country around Cromer,” pp. 119 and 126.

The theory of the gradual formation of overfolds and overfaults in a stratified system is thus developed by Professor Heim:—

Wherever a stratified rock series is subjected to the lateral horizontal thrust of the earth’s crust, a fold is originated. This fold consists of two opposed and symmetrical members, with more or less remote axes, viz. (Plate VIII. Fig. 1)

At the conclusion of my last paper on the Cheviot andesites and porphyrites (Geol. Mag. Vol. X. p. 262), I called attention to the close resemblance between the Cheviot hypersthene andesite (or porphyrite) and a rock from Steinerne Mann, Nahe, which has been called a proterobase. Both rocks are black in colour and consist macroscopically of glassy felspars (Mikrolin) imbedded in a groundmass which has a resinous or semi-resinous lustre. Microscopically they consist of two generations of felspar, pyroxene mostly rhombic, magnetite, and a glassy base with various devitrification products.

Professor Hughes in a brief but very valuable paper in the July Namber of this Magazine calls attention to a class of breccias of so much importance to the geologist that I am tempted to make a summary of notes that have been accumulating for some years and present it by way of a supplement. These breccias, produced in situ by mechanical forces, and subsequently modified by chemical, are very liable to mislead the student, andit is on this account (having myself been so misled in former, and often puzzled in recent years), that I call attention again to the subject—of what perhaps sufficient notice is not generally taken in text-books of geology.

In my brief paper published in this Magazine for 1880 (Decade II. Vol. VII. p. 404), I mentioned that pebbles of felstone were not uncommon in the Bunter conglomerate on the northern part of Cannock Chase. Since that time, as opportunity has occurred, I have been making a more special study of these pebbles, and think it may be worth while publishing a description of some of the commoner varieties, as a contribution to the lithology of this interesting deposit and a help to the determination of the question of the origin of its material. I believe that I have observed most of the varieties, which commonly occur in the district, but do not pretend (for circumstances have not allowed of this) to have made anything like a complete collection. Many of my specimens have been derived from the broken materials spread upon some roads newly made over the portion of the Chase in the vicinity of Rugeley, but several of them were obtained in a large pit in the Bunter itself, by the side of the railway on the road to Hednesford, and I was able by a careful search in it to identify most of the varieties that I had collected elsewhere. I cannot say that erratics are absolutely unknown in this district, but they are extremely rare, and there is practically no danger of making a mistake as to the source of the pebbles. These pebbles of felstone (to use an inclusive term) appear to be by no means rare. I think one could hardly search a couple of square yards of a newly “metalled” road without picking up a fragment. Now and then specimens are found with a dark ground-mass, and occasionally one which seems to be an indurated felspathic breccia; but in the majority there is a certain common character, though there are many varietal differences. These have a compact ground-mass, varying from a pale brick-red (the commonest) to some tint of pinkish-grey.

Since geology entered the order of exact sciences, it has been acknowledged by all those, who thoroughly studied it, that the history of the earth is to be divided into three great periods, which have been called, after the faunas they contain, Palæozoic, Mesozoic and Cainozoic. Indeed it could not escape the eye of the palæontologist, that between the marine faunas of the Permian period and the Trias on one side, and the Chalk sea and the Eocene period on the other, there is a greater difference than between the animal world of any of the other periods. In the transition-period between Permian and Trias, Corals, Cephalopods, Reptiles, etc., underwent an astonishing change; thousands of forms seemed to have perished, thousands of new ones appeared; in the succeeding time, shortly after the commencement the fauna of the Mesozoic seas showed, on the whole, quite another stamp, than that of the Palæozoic seas. A quite undisturbed development seemed to have reigned from Silurian to Permian, and there seemed to have been a sudden interruption of that development during the Permian period. Again, there followed an era of the most quiet and peaceful evolution during the Triassic, Oolitic and Cretaceous periods, where the connection between the several marine faunas seems to have been an uninterrupted one; then, at the end of the Cretaceous period, the marine fauna underwent a new change. The dawn of a new time (Eocene) begins, thousands of forms again disappear to be replaced a second time by new ones, as had occurred during the Permian period. Again, the Cephalopods seem to have been the class against which a war of annihilation was directed, and in their place the Pelecypods and Gasteropods take the leadership in the new era. The Enaliosaurians having reached a high development die out entirely and the Crocodilians retire to the rivers. The Secondary fauna gives way to the Tertiary, bearing a thoroughly new stamp.

IV.—Brachymetopus, M‘Coy, 1847.—General form elliptical; head-shield semicircular, and slightly pointed, about one-third wider than long; glabella small, somewhat elevated, one-third the width of the entire shield, and about one-half the length, having a basal lobe on each side, but no short lateral furrows on the glabella; neck-furrow distinctly marked, equal in width to the posterior border of free cheeks; eyes small, smooth, equal to half the length of the glabella; no facial suture visible, only the axal furrow surrounding the glabella and the neck-furrow; free-cheeks slightly convex, nearly twice as long as they are broad, with no visible suture separating them from one another in front of the glabella; margin broad and slightly grooved, angles of cheeks produced posteriorly into spines. The entire surface of the head covered irregularly with a small bead-like ornamentation.

In the August number of this Magazine, Mr. Howorth has challenged the view which I have advanced of the origin of the Loess (in common with the intrusive cave earth, the Warp of Trimmer, and the Trail of Fisher), from the slide of the upper and annually thawing layer of the permanently frozen soil, in the parts beyond the limit of the land-ice during the major and minor glaciations; or, as regards areas covered with sea during the major, from this process during the minor glaciation only.

The Coquet.—Blindburn.—A dark-grey compact rock with an irregular fracture. A few small scattered felspars may be recognized. Red streaks and blotches occur. Under the microscope two generations of felspar may be recognized; the larger porphyritic crystals abounding in inclusions of the ground-mass of the rock, while the smaller and later crystals are comparatively free from inclusions. Both kinds are somewhat altered, small portions here and there showing aggregate polarization, while the main mass of the crystals gives definite extinctions. The pyroxene has almost entirely disappeared. Sections of characteristic form may however be distinctly recognized. These are now principally occupied by an aggregate of quartz granules or a mixture of quartz and chalcedony; but here and there fibres of a brilliant and peculiar green mineral occur scattered throughout the quartzose aggregate, and these doubtless are an alteration product of the original pyroxene. Iron oxides are comparatively rare in this rock. The ultimate base is a brownish isotropic and minutely granulated substance. Under the highest power at my command (1000 diameters) the granulation cannot be resolved, and I am therefore not able to say that any clear homogeneous glass is present. Veins containing quartz and calcite occur in the rock.

In the last volume of the Geological Magazine the question concerning the origin of the Loess has been discussed by several authors in a minute and rather excited manner. Mr. Howorth has firstly expressed his opinion on that question in the Magazine for January and February, 1882, and he there combats the theory of the formation of the Loess as set forth by Baron Kichthofen (China, Bd. I., Berlin 1877). This distinguished geographer and geologist found himself compelled to explain and defend his theory in a detailed letter to the Editor of the Geological Magazine for July last, in which he enumerates and discusses the most important arguments of his theory.