In pressure-modified gneisses and schists certain minerals are often distinctly secondary in formation; actinolitic hornblende replaces ordinary hornblende in a gneiss, as on the southern side of the St. Gotthard Pass (31), or in a dark mica-schist, as in the Binnenthal (32), or a tremolite appears in marble near the Campolungo Pass (33). A mixture of crushed hornblende and felspar gives rise to a biotite, small flakes of which may be built, like bricks, into a newly-formed large crystal of hornblende, especially towards its exterior (34). Glaucophane in hornblendic rocks, such as diorites and eclogites, is often a secondary mineral (35), some constituents derived from a crushed soda-felspar having combined with those of the original hornblende. Rather large biotites have formed in a dark mica-schist in the Binnenthal, and here also some of them have been developed at right angles to the main pressure, but others in the direction of it (36). Scales of chloritoid, sometimes a third of an inch in diameter, are secondary formations in some gneisses and chloritic schists, and kyanites in some micaceous schists suggest a possible reconstruction of an original mineral. Chlorite itself is a mineral of secondary origin, and such rocks as smaragdite-euphotide (37), saussuritic gabbro, and possibly even ordinary gabbro are all more or less altered from their original condition, and in some at least of these cases pressure may have been a factor in the change.

It is scarcely necessary in this Magazine to insist upon the vital importance of potash, or upon the reasons which led to the former economic dependence of our own and many other countries on German resources. The shortage of potash, which arose as a direct consequence of the outbreak of war, became more and more accentuated until the latter part of 1917, when production from various revived and newly discovered sources began appreciably to relieve the then seriously acute position. In 1913, the last complete year of the older conditions, over £900,000 worth of potassium salts were imported from Germany by Great Britain, against imports of only half that value—much of which was cream-of-tartar, a byproduct of the wine industry—from all other countries. It is now safe to say that the German monopoly is completely broken, partly because of the return of Alsace to France, and partly because of the discovery of new deposits, and the successful development, under the stimulus of war conditions, of new methods of potash recovery from sources formerly unremunerative or unsuspected. The purpose of this article is to pass briefly in review the chief sources from which potash is, or may be, profitably extracted, other than those of the famous German deposits, which already have a voluminous and familiar, or at least readily accessible, literature.

It is these which afford the justification for any comparison between Sinocystis and Megacystis. Those of Sinocystis are, it will be remembered (antea, December, 1918, p. 534), a transversely elongale peristome, a hydropore-slit approximately parallel to the peristome, a gonopore to the left of the anal plane, and a hexagonal or pentagonal periproct. These openings, though differing in details, are in number and position essentially similar to those of Aristocystis. Hitherto there has been much uncertainty as to the positions, and even the presence, of the hydropore and gonopore in Megacystis. It will here be shown that both are present, and that all four openings have much the same relations as in Aristocystis and Sinocyatis, especially the latter.

The main feature of the geology of Drake's Island is the association of volcanic rocks with marine limestone of Mid-Devonian age. The Geological Survey memoir by Mr. W. A. E. Ussher attributes the discovery of the volcanic rocks to Mr. R. N. Worth. Mr. Ussher leaves their precise nature, “whether lavas or tuffs,” somewhat in doubt, but states that they are “most certainly contemporaneous”. As a matter of fact both lava and tuff occur, and are definitely distinguishable.

The well-known section alongside the Great Northern Railway just north of Sandy Station shows a total thickness of about 50 feet of ferruginous sands with occasional concretionary ironstone bands, resting on the Oxford Clay. This is therefore the lowest portion of the Lower Greensand. Numerous specimens from different levels in the exposure have been collected and examined, but they were all found to be very similar, and as a matter of fact not very interesting, so that a short description will suffice.

The general behaviour of the Scandinavian ice-sheet which spread over the North Sea at the climax of the Glacial period is fairly well known. Numerous erratics show that it reached the coast of Yorkshire and the eastern counties of England. Farther north no erratics have been found, but Dr. Jamieson and others have shown that it approached the coast of Aberdeen. Dr. Croll and Drs. Peach and Horne have shown that it forced the Scotch ice flowing eastward from the Moray Firth to turn in a northerly and north-westerly direction across the northern part of Caithness and over the Orkneys. They concluded that ice from the Christiania district must have passed a few miles to the north of the Orkneys. This is well shown in the chart attached to their paper and also in Professor James Geikie's map. The occurrence of a few Scandinavian erratics in the Orkneys would confirm these deductions. The only erratic recorded from Orkney which may be of Scandinavian origin is the Saville boulder described by Professor Heddle, Drs. Peach and Horne, and Dr. J. S. Flett.