The results of gravity surveys over various exposed and buried acid intrusions are summarized. Some sample density determinations are discussed. It is found that the acid intrusions considered are almost invariably associated with negative Bouguer anomalies, which are certainly often caused by direct density contrast between the less dense acid intrusive, and the denser country rock. This has two immediate implications. (1) Large negative Bouguer anomalies over “granites” may suggest magmatic origin. (2) These gravity anomalies, supported by seismological and seismic evidence, and the petrological distribution of igneous rocks, lead to the postulation of a denser “metasedimentary” layer overlying the “granitic” layer. The bearing of this on the mechanism of intrusion is briefly discussed.

It is shown that “Hutton's Unconformity” on the Isle of Arran has been misinterpreted. The assumed plane of unconformity is in reality the plane separating the Dalradian schists from the upper-most zone of schists impregnated with and cemented by calcareous material. The true plane of unconformity is situated some 4 feet above this plane.

As is well known the northern face of Garbh Bheinn, which rises from Loch Leven east of Caolasnacon farm, is occupied by a “very obvious asymmetric downfold” of inversion Eilde Quartzite (Hardie, 1952, p. 273; Bailey, 1934, p. 485). The inversion is established by current bedding and is unquestioned. The Eilde Quartzite here floats on Eilde Schist, younger than itself. The occurrence marks the western end of the Kinlochleven Inversion, one of the most remarkable geological structures known to science.

Seven species of ammonites from the Lungma Limestone of Tibet are described and figured. The assemblage is Middle Bajocian, of the Sowerbyi and Sauzei Zones, and possible also Humphriesianum Zone, and indicates that the formation is condensed. Its affinities are chiefly with European faunas, but it has one species in common with the Pamirs and another with Western Australia.

Tholeiitic rocks, which are well represented in the igneous history of the African Continent, occur as a dyke and related flow found by the writer in the north-east corner of Uganda. They outcrop in an area which is notable mainly for alkaline intrusions and lavas, so a brief attempt is made to explain the relationships and origins of the rocks in this limited area of the continent.

It is generally accepted that the continents contain more radio-activity than the Pacific floor. The two continents, Laurasia and Gondwanaland, would therefore expand the rocks below, relative to that floor. The plastic substratum under the continents would be forced higher in their centres than at their centres than at their Pacific margins. It would creep towards those margins and would carry part of the overlying granite to them, piling it high at their margins and thinning it at their centres. The plastic substratum would continually carry its heat to the cold Pacific substratum and render it plastic into which the continents would be impelled.

Small quartzite xenoliths scattered throughout the granodiorite are mantled by broad mafic coronas, the inner part of which is composed largely of augite and the outer part mainly of hornblende. The formation of the coronas is examined and some general features of magmatic reaction with quartzite inclusions are discussed.

A preliminary examination of Moine rocks containing rolled garnets from three widely spaced localities in the North-West Highlands indicates that the lineation in all cases is parallel to b. This is in accord with Phillips' theory that the metamorphism of the Moine schists was due to movement in a north-easterly or south-westerly direction. A Caledonian age for the metamorphism of the Moines therefore appears to be unlikely.

A technique for roughly evaluating the chemical variability within a suite of rocks is described and discussed in relation to the composition of the granite and quartzite of N. W. Donegal. The accuracy of this method is compared with more expensive chemical analysis.

In my recent paper on the Lochaber Series (Hardie, 1952), I gave detailed facts about the lithology of several of the stratigraphical units, and I concluded that the remarkable thickness variations were due to original sedimentary processes rather than to mechanical rearrangement. Sir Edward Bailey, in his paper in this current number of the Geological Magazine, strongly disagrees with my views, and argues in favour of sliding. In reply I would like to make the following three points.

After establishing average velocity of wind/average porosity curve for wind deposited sands, where it was shown that low wind velocity produces higher porosity than high wind velocity, further investigation was made and sands of various characteristics were used. It was established that the velocity of wind/porosity of deposit relationship is a more complicated function than was previously expected and some of the reasons are explained. The first indication of the influence of shape of the grain and the specific gravity of grains on the obtained results is registered. Further steps in the research are indicated.

A study of the structure and petrography of the limestones exposed at Hall Hill, in Bowland, enables the geometry of part of a Carboniferous reef knoll to be defined. The main features are a central mound-like core of unbedded, poorly fossiliferous calcite mudstone and a peripheral area of bedded calcite mudstones with original, depositional dips. Thick, well-bedded coarse crinoidal limestones were subsequently bedded over the underlying knoll.

The Breconian stage of the Anglo-Welsh Old Red Sandstone is defined. The Breconian follows the Dittonian and precedes the Farlovian. In Breconshire, the Breconian comprises the Senni Beds and the overlying Brownstones. The Senni Beds have yielded a fauna and flora of Siegenian-Emsian age; the Brownstones are apparently unfossiliferous.

Moraines which in one case at least contain striated boulders, show that, at the maximum of Quaternary glaciation, small, thin glaciers developed in the island of St. Kilda at certain favourable places. There is no evidence that the Hebridean ice sheet reached the island and no signs of raised beaches which would indicate recent emergence.

Gravity measurements in Durham and Northumberland in the region of the Alston Block are described, and their reduction as well as the accuracy of the results discussed. It is shown that the results between and near Newcastle and Durham are fully consistent with the conception of a horst, uplifted between the Ninety Fathom Dyke and the Butterknowle Fault. The observations along the valley of the East Allen, however, require an entirely different explanation. It is concluded that a closed area of negative anomalies occurs, centred near Wear Head. This is interpreted as due to a granite intrusion not yet exposed by denudation. The mineralization of the area is discussed and it is shown that it supports the foregoing interpretation.

A structural study of rocks of the Hecla Hook formation in the area of Forlandsundet of Vestspitsbergen reveals the presence of two B–axes. The earlier (B1) trends roughly east–west and affects only the Hecla Hook formation; the later axis (B2) trends roughly north–south, and affects also rocks of Carboniferous age. It is suggested that B1 is the main “Caledonian” axis in this area, and that B2 and the roughly north–south “grain” of the rocks concerned are Lower Tertiary phenomena.

Gravity measurements over the Northern Pennines indicate the presence of a buried acid intrusion under Upper Weardale, from which the mineralization there has originated. The negative Bouguer anomaly is presumed due to direct density contrast between the acid intrusion and the country rock, and is consistent with a magmatic origin.

In the search for large deposits of haematite and other feebly magnetic minerals, it is suggested that mapping the magnetic residuals may be of greater value than mere linear traverses. Not only is the method more suitable for exploring virgin areas, but it also affords a means of differentiating between the effects of large deeply buried masses and small objects at shallow depths. At the same time, the graphical expression of the results on the map becomes more easily intelligible.

The application of the method to known haematite ore-bodies in South Wales has yielded striking results and the extension of the survey into an unexplored area indicates the possibility of proving at least one further large haematite deposit.

The development of potash-rich pyroxene-bearing rocks around inclusions derived from the Appin limestone is associated with the transfer of magmatic silicon, aluminium, iron, and sodium. Calcium lost to the magma, by combining with further silicon, aluminium, and sodium to form a marginal zone rich in plagioclase, has left the magma enriched in potassium.

In the pelitic rocks of this classical section it appears that, chemically, a Fe2O3: Al2O3 ratio of about 0·40 is critical for the formation of chloritoid or staurolite. With this ratio both minerals are possible, but if the value exceeds a figure somewhere between 0·47 and 0·55 staurolite cannot form, a reddish-brown biotite appearing instead. Physically, a certain minimum temperature is necessary before staurolite can appear and below this chloritoid is the equilibrium phase.