The establishment, toward the end of the last century, of the fruitful conception of the “ cycle of erosion ” carried with it into general currency certain ideas which rest on no real foundation. Although few, nowadays, would be so rash as to doubt the validity of the cycle idea or to question its value as a principle in geology, few can demonstrate any truth in the accepted pictures of the later stages of the cycle. Geographical old age and peneplanation rest on nothing but pure deduction by a few great masters of geography and geology and a blind acquiescence by the rest of us. I say blind advisedly, because only blindness could prevent us from seeing some serious inconsistencies in the picture which have not been generally noticed. These inconsistencies have become increasingly evident in the last ten years. It is time to recognize them.

The Northumbrian Fault-block, forming the central part of the Pennine Chain, is a region of gently tilted Carboniferous sediments, bounded on the north, west, and south by major faultlines. It is divided naturally into two structurally complementary areas, symmetrically disposed to the north and south of the syncline of Stainmore. The present paper is concerned exclusively with the northern area, named by F. M. Trotter and S. E. Hollingworth the “Alston Block” (1928) and by H. G. A. Hickling the “Cross Fell Block” (1930). The first-named authors, who have recently completed a revision of the Geological Survey sheet covering the north-west corner of the block, have discussed in detail the structure of that district and have described the broad outlines of the tectonic history of the block (1928, 1932).

The mineralogical changes in green schists and related quartzofelspathic schists of sedimentary origin are discussed, and the following conclusions are reached as to the conditions of formation of oligoclase in these rocks:—

(1) Oligoclase normally appears as a product of dynamothermal metamorphism at relatively high grades such as prevail in the zones of almandine and perhaps kyanite. It is accompanied either by deeply-coloured hornblende, hornblende and biotite, or biotite and muscovite, according to the chemical composition of the rocks in which it occurs.

(2) Sodic oligoclase containing 10 per cent to 15 per cent of anorthite may occur with pale aluminous hornblende in green schists lying within the more strongly metamorphosed portion of the chlorite zone. The rocks in question are low in potash and have been formed by reconstitution, at a higher grade, of chlorite-epidotealbite-schists containing calcite. This oligoclase-hornblende association is not to be confused with the actinolite-epidote-albite-chlorite assemblage which is formed at any grade within the zone of chlorite, by direct reconstitution of basic igneous rocks without change in bulk composition and in the absence of CO2. A slight modification of Tilley’s subdivision of the green schist facies of Eskola is therefore introduced.

(3) A zone of oligoclase representing a grade of metamorphism higher than that attained in the biotite zone, may be recognized for quartzo-felspathic schists of appropriate composition and for many green schists, in areas of progressive regional metamorphism. In the latter case, blue-green hornblende often accompanied by biotite is also present.

(4) Oligoclase or more calcic plagioclase and deeply-coloured hornblende form readily during purely thermal metamorphism of only medium grade in the absence of stress. This accounts for the irregular distribution of both these minerals in districts where purely thermal and regional metamorphism have both occurred during the same period of orogeny.

The geological succession of the rocks of the N’Changa District is so typical of that of the Northern Rhodesia Copper Belt as a whole, and indeed of much of the Colony of Northern Rhodesia, that it is felt that a summary of the sequence of events which together make up the geological history of the district may serve as a contribution to the geological literature of the general Northern Rhodesian field. For a fuller account of the details of the petrography and mineragraphy of the rocks and ores of the N’Changa District reference should be made to Bancroft and Pelletier (1929), and Jackson (1932).

The first crossing of the Greenland Ice Cap by Fridjof Nansen in 1888 had shown that the southern part was a flattened dome rising to a height of 2,720 m. Crossings in 1912 by the Danish expedition of J. P. Koch and A. Wegener and by a Swiss expedition under de Quervain proved that there was a northern culmination, reaching to a height of at least 3,000 m., which was separated by a saddle of about 2,500 m. from the southern culmination traversed by Nansen. The form of the Ice Cap determined by these three crossings and by other expeditions near its margin of Rink, Jensen, Baron Nordenskiold, Peary, Gaarde, Mikkelsen, Rasmussen, and L. Koch, has been summarized in sketchmaps by L. Koch (1923) and de Quervain (1925). In the year 1930–31 several expeditions were simultaneously making further contributions to our knowledge of the Greenland Ice Cap. (See Fig. 1.)

It is believed that the “ beef ” in the shales-with-“ beef ” resulted from the leaching of the CaCO3 of a fine porous marl by a groundwater solution, and its subsequent redeposition. The initial redeposition was about the grains of calcite along bedding planes or similar divisional openings, and, as more material was added by the solutions moving to these planes, each original grain developed into a fibre in the layer of “ beef ”. Growth was from both sides, but took place faster on the upper side because the dominant movement of the water was downward. Growth stopped due to the exhaustion of the supply of CaCO3 in the marl or CO2 in the solution. The thin paper-shales between the layers of “ beef ” may represent the concentration of the original clay of the marl. This explanation of the origin of the “ beef ” would probably apply to other fibrous deposits of calcite, also.

WHEN a bedding-surface is faulted, a large number of quantities, of more or less significance, may be considered.

The elements involved are: (1) the fault-surface, (2) the net relative movement along it, (3) the bedding-surface, and (4) the surface of outcrop or measurement.

While accompanying the Oxford University Hudson Straits Expedition in 1931 to Akpatok Island in Ungava Bay, North Canada, the writer found that in the horizontally bedded limestones of Ordovician age one stratum alone was graptolitiferous. This contained a vast number of individuals in all stages of development, nevertheless all of the same species. When treated suitably with acid, specimens could be isolated from the matrix and thus a complete ontogeny has been worked out.

When dealing with the Scottish species referred to Allagecrinus (1932), it was a matter for regret that during the course of a long examination of the finer residue from washed shale from No. 1 Bed, Invertiel, among hundreds of tiny specimens the majority of which belonged to A. scoticus or A. elongatus, I had only been able to obtain two examples of the adult A. austinii.

PETROGENIC problems concern the processes and effects of adding to magma, or subtracting from it, rock-forming substance in general. Increment or loss of silica alone entails relatively simple mineralogical consequences. The more intricate problems concern the addition of associated material (notably alumina, the Ro-oxides, alkalies, and fluxes) in varying relative proportions, and at any stage in the evolution of rest-magma. These additions tend either to promote, counter, or otherwise modify the prevailing trend of differentiation in magma thus augmented.

The age of the Culm Measures of North Devon and, in particular, those of the Bideford Area, with which this paper is concerned, has long presented a difficult problem.

As early as 1875, Michel-Lévy made what is believed to be the first reference to that intergrowth of plagioclase and vermicular quartz which Sederholm later (1897) named “myrmekite”. In spite of its early recognition and characteristic appearance, however, there was for long no general agreement as to the geological significance or even the exact nature of the intergrowth. It appeared to be confined to the granitoid plutonic and metamorphic rocks, Becke (1913) having categorically stated that it does not occur in “eigentlich vulcanischen Gesteine”, so that it was with interest that the author recently (1932) recorded its occurrence in an Upper Devonian meta-toscanite from Marysville, Victoria. This does not conflict with Becke's statement, since the rock in question has suffered metamorphism by an intrusion of granodiorite, and is therefore not an “eigentlich“ volcanic rock. Nevertheless the mode of occurrence is unique, and the history of the toscanite has been elucidated with sufficient detail to allow one to infer with some accuracy the conditions under which the myrmekite was produced. In the following account, the myrmekite, biotite-quartz-symplektite, and biotite-dactylite in the subjacent granodiorite and neighbouring adamellite bodies, as well as the myrmekite in the meta-toscanite, are described.

In his description of the older rocks of Kintyre the writer has described in some detail the field characters of the Green Beds of that peninsula. Many difficulties were met with in the southern part of Kintyre where the rock-groups are repeated by folding. The chief of these difficulties were occasioned by the knowledge that schists identical in composition and appearance to the Green Beds occur at many different horizons below the Erins Quartzite.

While investigating the problem of coastal changes in South Wales, and examining 1 the area of the Merthyr Mawr Warren (Fig. 1) for this purpose, the differences, observable in the surface conditions to-day, and evident in the records of the past, between the areas east and west of a line approximating to the Burrows Well stream, suggested that the relatively recent physical history of the two sections of the area had not been similar. The greater width in the east suggested recent accumulation in this section, and the presence of what appeared to be successively formed littoral dunes pointed to a relatively recent phase of prograding, while the topography made it possible that these changes were related to the mouth of the River Ogmore.

Raised beaches and terraces generally are a common feature of the coast scenery of the Channel Islands. An attempt is made here to systematize them and to correlate them with other evidence of old base-levels and, very tentatively, with similar terraces elsewhere. The scattered descriptions in the literature have been brought together and detailed field-work, including measurements, has been carried out in Jersey. The main object of the paper is to give an ordered presentation of the facts as a contribution towards the attempts, now being actively pursued, to co-ordinate the drift deposits of north-western Europe. Any excursion beyond the bare facts is made chiefly in the interests of coherence, and many possible and even obvious theoretical conclusions have been omitted. The history of the subject shows that this does not matter as readers will be able to supply immediately all the ideas that have occurred to the writer and many others besides.

In 1930 Willard Berry published a paper on the Lepidocyclines of the Atascadero Limestone,1 for which he erected five new species, two of which were megalospheric and three microspheric.

The coral capped or fringed islands of the tropics afford many problems for students of the later formations. In the West Indies each island differs from another in structure. Barbados stands alone among them in its seaward position, the general Iniformity of its covering of coral rock and the height, 1,100 feet o which the coral rock has been raised. The formation of this oral rock, which reaches 240 feet in thickness, its uplift, the denudation of it off the Scotland area, and the deep ravining and erosion of both it and the Bissex Hill beds, Oceanic chalks, and Scotland Seeds is entirely so far as one can ascertain a feature of Pleistocene time.

The rock specimens described in this paper were collected by N. W. Pirie on the Cambridge Spitsbergen Expedition of 1930,1 and by the writer on the second and larger expedition of 1932. They represent an area forming the “neck” of Central Spitsbergen between Klaas Billen Bay to the south and Wijde Bay to the north, together with an area to the east and north-east of the Mittag-Leffler Glacier, extending northwards to the upper portion of the Lomme Bay Glacier, thus including the Stubendorff Mountains to the east of Wijde Bay and the western flanks of the Chydenius Range. The 1930 expedition started from the mouth of Ebba Valley in Petunia Bay and reached Wijde Bay by way of the Ebba and Mittag-Leffler Glaciers; after reconnoitring part of the Stubendorff Glacier they returned over the Mittag-Leffler and Ragnar Glaciers, passing to the north-west of Mount Hult. Most of the ground was again covered by the 1932 expedition, but in addition a sledge party reached the highland ice of Garwood Land at the head of the Ebba Glacier, turned north along the eastern margin of the Mittag-Leffler Glacier system and passing to the west of the Newton-Chernishev massif succeeded in carrying out topographical and geological observations on the Lomme Bay Glacier, though these were much curtailed by bad weather. On the return journey the party made their way down the “Vallee de Martin Conway”, crossed the divide between the Mittag-Leffler and Ebba Glaciers, and reached Petunia Bay by the same route that they had followed on the way up.

A general description of the drifts of Gower has been given in the memoirs of the Geological Survey,1 in which, however, no distinction was made between deposits of different ages. But it has long been known that there are at least two series of Glacial deposits in South-Western Britain, though until recently their relative extents were only surmised: in South Wales the relations of the drifts have been determined only within the last few years.2 As a consequence of this recent work it is clear that the Newer Drift does not extend into Gower much beyond the Sketty-Fairwood-Mumbles neighbourhood, and while the margin of this Newer Drift as determined by Charlesworth may be questioned in detail, especially further west along the Towy Valley,3 yet it is at least certain that the greater part of Gower is (or was) covered by Boulder Clay and gravels of the older drift. The general absence of deposits characteristic of terminal moraines, the “ mature ” topography, and the great amount of erosion that the drift has suffered are sufficiently distinctive, even apart from the extensive mounds of sand and gravel that mark the boundary of the Newer Drift further east.