Summary and Comparison with Other Areas in Scotland. Limestones in Ardgour are found to vary considerably in chemical and mineral composition. They have been subjected to high-grade metamorphism either dynamic (regional) or thermal, or sometimes to both. The dioritic intrusion has been responsible for the thermal alteration but does not show any widespread or conspicuous changes which might be due to contamination with limestone, although a certain amount of chemical exchange is apparent at some points of contact between the two. Mineral and chemical changes in some of the limestones have resulted from the metasomatizing action of solutions, the source of which is as yet uncertain. The various limestone types are found to exhibit a number of analogies with the Deeside limestone investigated by Hutchison and their petrography has been worked out in some detail.

Apart from certain hornblendic types in Central Sutherland, scapolite has not been recorded in the Moine Series. In Ardgour it has a wide distribution in the limestones associated with the diorite-gneiss. Wollastonite has not been recorded elsewhere in the Moine Series. Its distribution in Ardgour is like that of scapolite; and this applies also to prehnite. It must be remembered when thus comparing the Ardgour limestones with otters in the Moine Series firstly that these have not yet been studied in detail; secondly, that they are comparatively rare, and lastly, that there is doubt regarding the systematic position of some of the “Lewisian inliers” wherein limestones occur as a considerable proportion of the paragneisses. Scapolite, according to Flett (26) is a characteristic mineral in these rocks. Wollastonite occurs also as, for example, in the Glen Urquhart “inlier” (Cunningham-Craig, 27). In the Lewisian gneisses of Coll prehnite has a wide distribution and scapolite also is of frequent occurrence (Bailey & Eyles, 28). Pyroxene-amphibole rocks similar to those in Ardgour are found in Coll, Glen Urquhart, and as xenoliths in norite (Read, 29). The mineralogical character of the limestone is, therefore, in support of the conception of their forming part of an inlier in the Moine Series. The writer hopes to publish shortly a more detailed study of the geological problems of this area.

It is difficult to draw the line between aridity and semi-aridity, just as it-is difficult to differentiate between humid and semi-arid climates as they affect the development of landscape forms. No hard and fast divisions based on rainfall figures can be adopted. Evaporation, in part controlled by temperature, and the seasonal distribution of rainfall are also important factors. “The rainfall regime is divisible”, according to. Bryan, “into the episodic and the periodic. In the episodic type rain falls in storms that are highly variable in intensity and are scattered through the year; in the periodic type precipitation is concentrated in one season, either summer or winter. In areas having the periodic type vegetation is adjusted to the wet season, and a relatively greater vegetative cover is possible with low rainfall. The Mediterranean region and California have the periodic type of rainfall, with winter maximum and mild temperatures. Thus in many sub-areas the land forms under mean annual rainfalls of 15 to 20 inches are very similar to those of humid regions, although the soils … are quite like those of other arid regions. The episodic rainfall, because of its variability in time throughout the year, is less effective in promoting growth, and the vegetative cover may be so scant with rainfalls of 5 to 7 inches that geomorphologically the region is essentially a desert. Episodic rainfall as high as 15 to 20 inches may produce steppe conditions. … In general the warmer areas have a relatively scantier vegetation with the same rainfall regime. Including this relation all varieties of hot and cold deserts or semi-arid climates are possible (2).”

In several papers by the present author alone or in collaboration with Dr. J. E. Hemingway, mention has been made of the abundance of the titanium minerals, rutile, anatase, and brookite, in the Middle Jurassic sediments of Yorkshire. One of these papers dealt with brookite crystals from the Dogger, and the present one will describe briefly the types of rutile crystals from the same formation; partly because these show interesting peculiarities, and partly, as a subsidiary object, because it has appeared during this investigation that the descriptions given in most of the books of reference of sedimentary rutiles are somewhat inadequate, several striking features found to be widely prevalent not being mentioned in any of them, while other points are dealt with very briefly by most authors. A beginner in sedimentary petrography, confronted with a heavy mineral concentrate of this kind, might find considerable difficulty in identifying the crystals of rutile.

Grève de lecq is situated on the north coast of Jersey, about 2½ miles from the western end of the island. On each side of the bay is a lamprophyre, discovered by Dr. A. E. Mourant, and the two dykes are so much alike in mineral composition and texture that separate description is unnecessary. The country rock is granite.

The Blattoids, or early cockroaches, are on account of their mode of life, far more numerous as fossils than any other Coal Measure insects.

It seems late in the day to ask the International Commission to standardize the use of Rhacophyllites in the interpretation commonly accepted for over half a century, but until I discussed this genus last summer with Dr. S. W. Muller, Stanford University, California, in connection with work on Lias ammonites, I was unaware that it offered a nomenclatorial problem or that this was incapable of a simple solution on the basis of the existing rules of nomenclature. A discussion of the difficulties encountered may not be out of place in this series, and I hope to show that this is indeed one of the special cases in which standardization provides the only fair solution.

The Upper and Lower Estuarine Series in the East Midlands contain a number of layers of carbonaceous shale or clay and in many cases roots can be seen extending downwards in the underlying deposits. Except for plant-remains these carbonaceous layers are for the most part barren. Samples supplied by Mr. Linsdall Richardson were examined by Professor Harris and found to contain small fossil plants of types which appeared determinable and thus of possible stratigraphic value. Mr. Richardson collected other samples which he sent together with stratigraphic notes; Professor Harris handed me the material for investigation.

In the type area the Ludlow Rocks generally have been divided into Lower Ludlow Shales, Aymestry Limestone, Dayia Shales and Whitcliffe Flags in upward sequence. The Dayia Shales are characterized by the presence of enormous numbers of Dayia navicula (J. de C. Sowerby). This preponderance of D. navicula in the shales immediately above the Aymestry Limestone has caused a tendency to regard beds in other localities containing this fossil as being on the same stratigraphical horizon in spite of the character of the accompanying fauna. In two recent papers on the Ludlow Rocks of the Welsh Borderland (Straw, 1937, and Earp, 1938) it has been shown that D. navicula ranges through at least 3,000 feet of strata, occurring commonly throughout this great thickness and outlasting more than one change of fauna. Although, in this area, the brachiopod ranges from the zone of Monograptus nilssoni into the Upper Ludlow it has not hitherto been recorded below the Aymestry Limestone in Shropshire. This gap in our knowledge is now filled by the discovery of specimens in Lower Ludlow Shales exposed in a small quarry 40 yards north-east of Stokewood Cottage, which is on the west side of the railway line a little over a mile south of Craven Arms. The quarry shows about 15 feet of nodular shales with thin limestone seams. The commonest fossils are Chonetes laevigata (J. de C. Sowerby), C. minima (J. de C. Sowerby), and Stropheodonta filosa (J. de C. Sowerby) which occur in large numbers on some of the bedding surfaces. Other fossils are Stropheodonta euglypha (Dalman), Delthyris sp., Orthoceras sp., Dalmanites sp., and a plectambonitid. Dayia navicula seems to be confined to a thin layer on the north side of the quarry. Graptolites referable to Monograptus cf. chimaera occur fairly commonly. About 400 yards in a south-easterly direction another small quarry exposes Conchidium Limestone which is about 170 feet stratigraphically above the beds in the first quarry.

During the summer we paid two visits to the site of a sewer trench that was being dug from Aylesbury along the London Road towards Tring. At the time of our visits excavation was being carried on in the village of Aston Clinton.

The record by Dr. Rastall (1) of new types of brookite from the Dogger of North-East Yorkshire prompts a note on the brookite of the Millstone Grit of West and South-West Yorkshire, since the brookite of this latter formation presents interesting features somewhat different from those presented by the brookite of the Dogger.

In the study of the structures acquired by sediments in the process of slumping, a knowledge of the probable state of consolidation of the materials is of some importance in forming correct views regarding submarine sliding and the conditions under which it occurred.

Holmes, Kossmat, and Hess have independently pointed out that basic to ultrabasic rocks are characteristic of the axes of geosynclines, whereas acid rocks do not occur at that stage of development. Conversely, acid intrusives enter after the contents of the geosyncline have been folded. A short time ago an exhaustive summary of this subject was given both by Bucher and Rittmann.

In recent years much work has been done in determining the quantitative—or more strictly “numerical”—composition of heavy mineral residues from sedimentary rocks in the hope of obtaining evidence as to whence the detritus was derived. It is clear that the petrological characteristics of the land mass whose erosion provides the detritus must always be an important factor in predetermining the percentage composition of the residue as we now find it. Yet the sorting action of the transporting agents (which tend to separate the heavy from the less heavy minerals) and of chemical agents (which, both before and after deposition, destroy some minerals and introduce new ones) may often be suspected of having a great or even a dominating influence upon the final composition of the residue. It is proposed in this paper to investigate by simple mathematical methods the probable effect of these processes and to do so along lines which have been suggested by the study of actual heavy mineral assemblages.

It will have been observed in our consideration of the physiography of the north-eastern corner of the Northern Frontier Province of Kenya Colony that there is strong evidence in support of the existence of fault scarps, which date their first uprising from the Jurassic age. The evidence in the Coast Province in the neighbourhood of Mombasa is not so clear, but if we examine this in the light of that from the northern frontier, it will be seen that there is a strong suspicion that the coast ranges, too, are horsts, dating their first rise from the Jurassic.

The origin of the West Cumberland haematites is one of those unsettled problems that have exercised the minds of geologists and miners for more than half a century. Theories have been evolved, but not one can claim general acceptance. It is not my purpose to discuss these theories here, but the consideration of one of them was directly responsible for the examination of the reddened Carboniferous rocks that form the subject of this paper. This theory, first advocated by J. G. Goodchild and later supported by Dr. B. Smith, may be stated briefly thus: The New Red Sandstone rocks were the immediate source of the haematites. From these rocks the iron was carried in solution to lower levels by the downward percolation of meteoric waters. The theory had the merit of explaining, not only the haematite deposits of the Carboniferous Limestone of West Cumberland, many of which occur beneath the New Red Sandstone Series, but also the reddened Carboniferous strata frequently found in North-Western England, beneath and fringing the base of the Permo-Triassic rocks.

It has been suggested that petrologists may be interested in a brief account of the Cambridge University collection of rock-slices, comprising at present some forty thousand slides. It had its small beginning sixty years ago, when microscopical petrography was still something of a novelty. Among the first in this country to use the new method of research was Dr. T. G. Bonney, then in residence at Cambridge; but the large collection which he gradually amassed came to us only at his death, and the earliest slides in our cabinets were made for E. B. Tawney, at that time Assistant to the Woodwardian Professor. The preparation of thin slices of rocks was not the comparatively easy and rapid process. that it is to-day (emery was the only abrasive used), and it was not unusual to give credit to the practitioner in published papers. The best known, if not the only one, in England was F. G. Cuttell; later it was customary to get the slicing done in Germany.

The discovery of an active oil seepage in Corallian sandstones at Osmington Mills, near Weymouth, led in 1937 to an examination of the adjacent Poxwell or Moigns anticline by geologists of the D'Arcy Exploration Company, a subsidiary of the Anglo-Iranian Oil Company, Ltd. The investigations, carried out by Dr. C. T. Barber in the earliest stages, and subsequently by the junior author, consisted of surface mapping assisted by pits, trenches, auger holes, and shallow bore-holes, and culminated in the drilling of a test well in the crestal area of the anticline. This note summarizes the more important information obtained with regard to stratigraphy and tectonics.

The “Tarskavaig-Moine” schists occupy a small area in the Sleat district of Skye, extending southwards from Tarskavaig to the Point of Sleat, a distance of about seven miles, with a maximum width of outcrop of two and a half miles between the coast on the west and structurally overlying formations on the east. Their tectonic relationships and petrographic characters were first described in detail by C. T. Clough in the Geological Survey Memoir on the North-West Highlands of Scotland (1, pp. 589–594, and pp. 618–621). The northern part of the outcrop falls in Sheet 71 of the one-inch geological maps, and is described in the accompanying memoir (2); the southern part falls in the unpublished Sheet 61. Later publications summarize these earlier discussions (3, p. 171; 4, p. 309; 5, p. 23); the last named includes a map of the whole outcrop, on a scale of two miles to an inch, simplified from manuscript maps by Clough. A summary of the tectonics and metamorphism has recently been published by Dr. E. B. Bailey (6).

In the brachiopod family Strophomenidae, it is recognized that various genera, of which Leptaena Dalman is a good example, may possess a foramen enclosed within the umbo of the ventral valve, near the apex of the pseudodeltidium (see Text-fig. 2 A). Such a foramen is presumably a pedicle-aperture, and bears a superficial resemblance to that of certain Telotremata in which the young pedicle emerged through the open delthyrium and subsequently resorbed the apex of the ventral valve and became enclosed dorsally by the deltidial plates. In the young stages of Leptaena, on the other hand, the foramen was entirely supra-apical and enclosed within the ventral protegulum and nepionic shell, though sometimes it later suffered resorption of its dorsal margin so as to become bounded by the pseudodeltidium.