The examination of the internal structures of Jurassic fossils is attended with considerable technical difficulties. Even in cases where the surrounding matrix is sufficiently friable for the development of the external surface, the infilling material is usually either thoroughly indurated or irregularly nodular in texture. Internal moulds may be readily procured, both by natural weathering and artificial processes. But such preparations, though adequate for the investigation of shallow impressions such as the muscle-scars of Pelecypoda, are of uncertain service for the study of structures with amount of peristomial circumference (reduced to a simple circle) built up by the two areas is approximately the same, but the interambulacral portion is entrenched upon by the branchial incisions. The ambulacra present a semi-elliptical margin to the peristome, while that of the interambulacra is more nearly semi-circular. The ambulacral pores, which are not crowded nor much displaced from their direct line, pass down near to the adradial sides of the branchial incisions, and curve round with the margin of their areas.

The Iguanodon has been known since 1825, when the genus was first described from teeth by Mantell. Odd bones and various associated portions of the skeleton have been found in England, and in 1878 the skeletons of many individuals were discovered in the Wealden of Bernissart, near Mons, Belgium.

In 1914 I published, in this Magazine, an account of “Some Problematical Structures in the Holectypoida”, indicating therein the presence of certain sunken features on the test-surface of “Pygaster” (Plesiechinus), Coenholectypus, and Discoides. Two series of depressions were described, of which one was wholly sutural in position, while the other was situated on the adoral ambulacral plates, and consisted of more or less sunken tubercles or granules. It is with the latter series of structures that the present paper deals. Although the title “problematical structures” remains appropriate, further work and more refined methods of preparation have made possible a more accurate description of them, and have considerably increased the area of their known distribution. Save for comparisons and passing references, the development of depressions on the tests of the Pygasteridæ and Holectypinæ will not be considered here. In Jurassic times, when these two groups were at their prime (in this country at least), sunken tubercles were in an incipient stage of evolution, and are in consequence very difficult to distinguish from their normal associates. It is therefore safer to deal first with the well-matured structures, as developed in Upper Cretaceous times. Moreover, the condition of preservation, and especially the character of the matrix, of Chalk fossils, make it easier to clean and stain the specimens without much risk of damage to delicate surface features.

Besides the series of Membraniporellæ last described there are several other Cribrilinidæ which develop a secondary aperture in the same way, and the next four species are instances.

The Javan fossil corals collected by the Austrian frigate Novara included a specimen on which Reuss (1866, p. 172) founded a new genus, Polysolenia. He described it (ibid., p. 172) as showing in the structure of its cœnenchyma “eine überraschende Ähnlichkeit mit Polytremacis und Heliopora”. “Das Cönenchym besteht aus langen, ziemlich dicken, geraden, neben einander liegenden Röhren.” These tubes, according to his account, occur in circles of six around a central tube. Reuss repeated (p. 174) that the cœnenchyma is composed of regular parallel tubes (Röhren), whereby it is closely allied to Heliopora and Polytremacis. He named it Polysolenia “nach ihrer röhrigen Structur”. Reuss' illustrations suggested some suspicion as to the accuracy of his description, since the dark parts of his figures might be interpreted as the original solid structures of the coral, and the light parts as the matrix. If so, the cœnenchyma would be trabecular and the septa a series of thin lamella. Reuss, however, was emphatic that the septa are thicker than the walls of the supposed cœnenchymal canals; and, if so, the light parts of the figure represent the original solid structures. If the coral had undergone a double change in fossilization Reuss' view was possible; and his statements that the circular rods are casts of canals were so positive that, though in 1900 I mentioned my doubts, I felt bound to dismiss them. So I accepted the fossil as a Miocene Helioporid, and as the name Polysolenia was preoccupied renamed the genus Octotremacis (1900, p. 302).

The name Pahang Volcanic Series was given by Mr. J. B. Scrivenor to those eruptive and intrusive rocks of the Malay Peninsula which are older than the Mesozoic granite, and the rocks were described by him in The Geology and Mining Industries of Ulu Pahang, 1911, ch. xi. As the name implies, the series is most strongly developed in Pahang, but it is also developed to a greater or less extent in Singapore* Island, Johore*, Negri Sembilan*, Selangor*, and Perak*, and possibly also in the more northern states, Kedah*, Kelantan*, and Trengganu*. The present account deals for the most part with the main development in Pahang, and most of the information was obtained on two trips, one to examine the railway-cuttings from Gemas* to Kuala Lipis, and the other to examine outcrops over a distance of about 100 miles in the rivers Jelai and Pahang, from Kuala Lipis to Mengkarak.

The characters of the apical system of a series of Holectypus hemisphæricus from the same horizon at two localities in Dorsetshire are analysed and described. It is found that the average relations of the plates of the system are different at the two localities, although certain numbers of identical forms occur at both. Out of 189 specimens (from both localities), 40 show serious departures from the normal type. These abnormalities are of three classes. One, the most prevalent, consists in the presence of madreporic pores on genital 3, in addition to the normal perforation of genital 2. This is regarded as a “progressive variant” in the direction of Discoides. The second, occurring in three specimens, consists in the interpolation of a supernumerary plate within the system. It is suggested that this may be either a “regressive variant” towards Acrosalenia, or a “progressive variant” towards Nucleolites (as illustrated by N.orlicularis). In neither case would this variation coincide with actual phyletic sequence, so that it is styled “parallel variation”. The third type of variant, seen in one specimen only, combines both the first and second types, and in addition shows an absence of genital 5 and a corresponding increase in the size of the posterior oculars, which meet round the back of the system. The variation in this specimen is interpreted as being “progressive” towards Discoides, “parallel progressive” or “regressive” towards Nucleolites or Acrosalenia respectively, and “progressive” towards Conulus. There are indications of a different series of variants in the Holectypus depressus from the Cornbrash. The high percentage of variation in the composition of the apical system of Holectypus is regarded as an indication of the evolutional activity of the genus, and of its near approximation in time and phylogeny to the common origin of many of the groups of Irregular Echinoids.

A Comparative study of the whole of the evidence concerning the Palæozoic floor beneath the South-East of England and the manner in which the various members of the Mesozoics are disposed upon it has led the present writer to conclude that the area, originally defined by Professor P. F. Kendall, over which the effects of the operation of a “posthumous” Charnian axis may be discerned, can be greatly extended, more particularly to the eastward. The evidence, indeed, strongly suggests the presence of a second Charnian axis beneath Suffolk, proceeding thence south-eastward to North France.

Mr. G. W. Bulman, in an essay on “Chalk Flints and the Age of the Earth”, states that Professor Owen regarded the layers of flint in chalk as “the remains of successive crops of sponges which grew again and again according to some periodic law”. Mr. Bulman then observes that the only periods affecting rock-formation are annual, and he suggests that sponge-growth might be rapid during the summer months and that free-swimming reproductive spores might be liberated towards winter, the old sponges then dying off. This implies that the water at the depths in which the sponges lived in our Cretaceous seas was responsive to climatic change, and that the sponges were equally responsive. The suggestion breaks down, however, on another ground, when its author points out that it demands the deposition of 3 or 4 feet of chalk in a year, so that the whole of the English strata above the Albian might have accumulated in about four centuries. Mr. Bulman thereupon remains hesitant and enquiring.

In a previous paper the writer briefly alluded to the evidence, as known from the deep borings in East Kent, afforded by the Palæozoic and Mesozoic rocks, of the operation of a posthumous axis of unrest, probably of Charnian affinity. This conception receives further support from a study of the special characters exhibited by the Wealden of East Kent and the nature of the unconformity between these strata and the Mesozoic and Palæozoic rocks underlying them.

During the last ten years I have published a series of memoirs on different questions concerning the morphology and biology of the Rugose Corals. In these memoirs I have elucidated the ground-form of the polyparium of the solitary Rugosa, the mode of its attachment to the substratum, the origin of the characteristic arrangement of the septa, and the origin of the fossuloe in dependence on this form and attachment. I have established the connexion between the form of the polyparium of the Rugosa (including that of the fossulse) and the life of these corals in definite environmental conditions.

In “The North American Crinoidea Camerata”, 1897, Wachsmuth & Springer discussed at length the various modes of partitioning the base, and attempted to give a morphological, if not a physiological, interpretation of the various appearances. In reviewing this part of their work (Geol. Mag., Sept. 1898, pp. 426–428) I contented myself with giving a summary of their views, corrected only in so far as facts of structure were concerned. This summary was reprinted in the Echinoderm volume of Lankester's Treatise on Zoology (1900, pp. 122, 123), although some of the theory involved in it was not in accord with the phylogenetic hypotheses expressed or implied in the taxonomic part of that work. Mr. Herrick E. Wilson has been more critical. He has brought Wachsmuth & Springer's interpretations to the bar of logic, of fact, and of physiological theory, and has found it necessary to replace most of them by a fresh series.

Leidleite and Inninmorite.—Typical rocks of these groups are as yet unknown in the Clyde area. A N.N.W. dyke at Barrassie Sands, near Troon (Ayrshire), has points in common with leidleite. It shows anorthite phenocrysts in a subvariolitic groundmass of acicular felspar and augite, enveloped in a partially devitrified glassy base. A north–south dyke at the north end of Loch Fad, Bute, may perhaps be regarded as a doleritic end-variety of leidleite (see Anderson & Radley, 1916, fig. 2b, p. 208). A pitchstone-like dyke from the Smurig Burn in the south of Arran has all the characters of leidleite, except that it carries rather abundant granular augite, instead of acicular crystals.

The very numerous Tertiary dykes of the Clyde islands (Arran, Bute, and the Cumbraes), and of the adjacent mainland and peninsulas, have been little studied either from the geological or petrographical point of view; but they are of great interest, not only in themselves, but as providing a link between the dykes of the better known areas of the North of England, and of Skye and Mull. The material is not yet gathered on which could be based a complete account of the series. The present paper is designed to present a full description of a hitherto unrecognized type of Tertiary dyke, typically exposed in the Great Cumbrae, and to indicate its relationships to other types already described from Mull and the North of England. Furthermore, a few other dykes from the Clyde area, all of basaltic composition, will be briefly described.

The New Hebrides group of islands was first fully made known to Europe by Captain Cook, who in the year 1774 spent forty-six days among them. Situated in the Southern Pacific, about 1,400 miles N.E. of Sydney, the total number of islands is nearly eighty, the largest of which has a coastline of 200 miles. The islands are mainly of volcanic origin and lie in a direction from S.S.E. to N.N.W. Volcanic action is almost exactly in the direction of the group of islands, and a line drawn from the volcano of Tanna in the south to the volcano of Tinakula in the north, a distance of 600 miles, would pass through the volcanoes of Lopevi, Ambrym, Ureparapara, and the boiling springs of Vanua Levu.

Almost due west of Mozambique Island, at a distance of about forty-two miles from the sea, the military road from Mosuril to Nampula crosses the Ampwihi River, an important tributary of the Monapo. During the dry season the stream is reduced to a string of stagnant pools, separated by long reaches of sand and gravel that here and there are interrupted by outcrops of the underlying formations. Throughout the greater part of its course the Ampwihi flows through a region in which gneisses persist with monotonous regularity, the only variation being that due to occasional intrusions of granite and of still later pegmatite dykes. At the point where the military road crosses the narrow channel a welcome diversion is introduced by the presence of a dark compact dyke about 10 feet in thickness. The dyke appears on the right-hand bank and crosses obliquely to the other side, taking a N.N.W.–S.S.E. course across the strike of the older rocks. Upstream, about seventy yards to the south-east, the Ampwihi bends to the south-west, so that it returns towards the dyke, which is again exposed across its sandy floor. The dyke was traced by Mr. E. J. Wayland in July, 1911, for a distance of altogether 200 yards, and was examined by Mr. D. Alex. Wray and later by myself during the same year. It is clearly the latest rock of the district, and is intruded along a line of fault, for in two cases pegmatite dykes seen on the eastern side are broken across and reappear on the western side with a well-marked northerly displacement.

During the past two years the teaching collection of rocks in the Geological Department of the Imperial College has been underre-arrangement, and in the course of the work the writer has had occasion to consider very carefully the principles on which igneous rocks should be classified. He is aware that in the present state of our knowledge any such classification must be tentative and experimental, and should be judged according to its general convenience, both for teaching purposes and for understanding the various problems that arise from petrological studies. The following article summarizes the conclusions arrived at, and while the writer must be held entirely responsible for all expression of opinion, he wishes to acknowledge his gratitude and indebtedness to Professor Watts and Dr. Evans, both of whom, in numerous discussions, have freely offered suggestions and criticism which have proved to be of the greatest value.

Included in a large series of marine fossils which I collected from the Cisco Beds of Uralian or Upper Coal-measure age at a well-known locality on the west bank of the Salt Creek at Graham, Young Co., Texas, are several fragments of a single very large nautiloid shell. These fragments had lain so long on the sea-floor before they were covered by mud that they have in many cases been much eaten into by sponges and worms, and are covered by adherent organisms, mostly Bryozoa. Attached to them, however, are twenty specimens of the remarkable Brachiopod which forms the subject of this paper. These specimens are in general perfectly preserved, and are easily freed from their surrounding clay by washing with a tooth-brush.

The recent paper by A. Holmes on “A Mineralogical Classification of Igneous Rocks” is an attempt to settle a matter which English-speaking petrologists ought to have tackled long ago. There seems, however, to be a disposition, on the part of British geologists especially, to leave the matter alone in the fond belief that some “natural” system of classification will presently be revealed to us whereby all our taxonomic doubts and difficulties will be dispelled. Nothing can be more unreasonable. The philosophic treatment of a subject must follow, not precede, the preparatory work of discriminating, sorting, and docketing; and the sharper the discrimination, the more thorough and orderly the sorting and docketing, the easier to make the philosophic digest. Hitherto petrographers have not discriminated well; we have not done our sorting in a methodical way; we have tied on labels in the most haphazard fashion; our house is in a state of dreadful confusion. It is true that through all the disorder we have caught fascinating glimpses of regularities and relationships; of connexion between this and that; but the deplorable fact appears that we are unable to test or verify any hypothesis, or to take a single confident step towards the philosophic treatment of our subject, until we put our house in order. We have got to do our sorting and docketing all over again, and do it methodically, and then only can we begin to look for the philosophy of the matter.