The greatest diameter of a Pecten is nearly always the height. It is easier to visualize the size of a shell from this measurement than from the length. Consequently in tabulating the dimensions of the species the height is first given in millimetres, followed by the length as a percentage of the height. Since in the vast majority of the ordinary species the shell is, except for the auricles of the right valve, subequilateral, no obliquity measurement is necessary as with the Limidae. Another redundant measurement in dealing with Jurassic Pectinidae is the inflation. This dimension is always such a small percentage of the height that accuracy of measurement without special apparatus is a matter of difficulty unless both valves happen to be joined, closed, and free from matrix. Even such differences as do exist can rarely be detected in allied species, such as might be liable to confusion in other respects.

Material—The six more or less complete specimens and twelve fragments to be described are preserved in a coarse ferruginous sandstone. They were collected by Messrs. C. Barrington Brown and R. A. Baldry, who supply the following particulars of horizon and locality, and to whom the author is indebted for the opportunity of describing this interesting echinoid.

About Easter, 1925, I noticed the curious course of the streams through the big deltas of Measand on Haweswater, and of Aira Beck on Ullswater. Both these streams, after having traversed about half the radial length of the delta, turn fairly sharply towards the head of the lake. This turn in such a pronounced degree is contrary to what one would expect.

The Bushveld Igneous Complex lately formed the object of a study by the Shaler Memorial Fund Expedition and some members of the staff of the Geological Survey of South Africa, the principal object being to ascertain and fix its relation towards the upper division of the Waterberg Sedimentary System. Their report, published in the Journal of Geology, would seem to furnish the necessary complementary data to fix the origin of the magmatic complex concerned, to a degree of extreme probability, as may be shown in the following.

The typoscript of this paper was found by me among my father's MSS., after his death on 11th April, 1923. There was evidence to show that it was written rather earlier than 1908, and it is obviously the first part of a paper which had been put on one side during the preparation of “The Pliocene Mollusca of Great Britain”. The typoscript ended with the heading “Floods of Miocene and Pliocene Periods”, but I have no reason to believe that this section was ever prepared. The three figures here reproduced were with the typoscript, but others which it had been intended to use in illustration of the paper have not been found.

In a mighty curve, convex to the west and north, the Central Alpine Zone trends from the Mediterranean to the eastern confines of Switzerland in the north-east, marked by a series of granite massives, the principle of which are: Mercantour, Pelvoux, Belledonne, Mont Blanc, Aar, and St. Gotthard.

In the bilateral symmetry of the Rugose corals it is the general form of the polyparium, presenting a cone bent in the form of an oxen horn, that strikes at once the observer's eye and obliges him to seek for an explanation.

Recently a mechanism allowing the escape of the heat generated by radioactivity in the basaltic under-crust of the earth has been proposed by Dr. Holmes, and a very similar one by Dr. Joly has gained wide attention. In these theories the excess heat generated by radioactive changes is supposed to be dissipated by an alternate fusion and solidification of the basaltic magmas assumed to make up the lower levels of the outer crust, the heat escaping through the floor of the oceans during so long a period of time that while, in the aggregate, the amount of heat thus passed out is very great, yet at no time is the temperature of the oceans sensibly affected.

In a series of memoirs by Burckhardt (1), Groeber (2), and Gerth (3), the stratigraphical sequence and structure of the Cordillera of South Mendoza has been lucidly described. On the basis of these memoirs, of my own field observations (12), and of the study of the large collection of rocks made by Dr. Gerth, I shall attempt in this paper to give a picture of the magmatic evolution of this part of the Cordillera of South America (35 to 37 degrees south latitude).

During the last two years a series of deep excavations have been made in the floor of the Aire valley near Skipton (on the border of sheets 92 S.E. and 92 S.W. 1 inch to 1 mile, Geological Survey). These have brought to light a hitherto unsuspected deposit of laminated clays of great thickness, which are of considerable interest in interpreting the events of the Glacial retreat in this valley. A. Jowett and H. B. Muff in 1904 published their work on the glaciation of the Aire valley between Keighley and Bradford, in the course of which they described three terminal moraines of the Aire glacier, at Tong Park, near Baildon, at Hirst Wood, about a mile and a half west of Shipley, and at Bingley; in the course of the paper they mention without comment the fact that above the Hirst Wood and Bingley moraines there is in each case an extensive flat of alluvial material, extending far up the valley. Although these have long been tacitly regarded as lake flats, the first confirmation was received in 1920 when the excavation of a deep trench in the flat half a mile west of the Hirst Wood moraine revealed a quantity of laminated clay underlying the undoubted river gravels. The excavation was only temporary, and unfortunately no measurements or deeper trials were obtained. Recently a trench above the Bingley moraine has been cut deep enough to show the laminated clay underlying the river gravels here as at Hirst Wood, and these two exposures have directed attention to the existence during late Glacial and post-Glacial times of a series of lakes held up by the terminal moraines left by the Airedale glacier. That such lakes existed has long been the opinion of most local geologists, but they have always been regarded as of brief duration, drainage being rapidly accomplished by breaching of the moraine barrier, or, in the Hirst Wood case, by super-deepening of the cut round the north end of the moraine, a cut probably initiated in late Glacial times. The material from the Skipton excavations indicates that these lakes were of far longer duration than previously suspected.

As stated previously the aim of this paper is chiefly to call attention to the differences between the mineral assemblages of the Downtonian, Dittonian, and Farlow Sandstone beds of the Old Red Sandstone, particularly when the percentages of the different mineral grains are obtained by accurate counting. Further work will show how far these investigations may be correlated with the examination of the rocks in adjacent districts, and the author suggests that a similar calculation of percentage figures on the minerals of such deposits may assist in indicating more definitely the sources from which they have been derived.

Since writing the first report on the arthropods of the Rhynie Chert beds (see Ann. Mag. Nat. Hist. (9), xii, pp. 455–74, 5 pls., and 13 text-figs.) some additional specimens of Palaeocharinus have been collected. A few examples are fairly complete and well preserved, showing a considerable amount of structural detail, such as the chaetotaxy, claws of the legs, ornamentation of the chitin, eyes, etc. An account of the lateral eyes is given below. We also include notes on a supposed insect and another fossil arthropod which we refer with doubt to the aquatic Merostoma. All the illustrations in this little paper have been drawn by Miss Violet Borrow, A.R.C.A., with the aid of a camera lucida under our personal supervision.

The Old Red Sandstone occurs in Gower in several inliers which form hills rising above the undulating plateau of Carboniferous Limestone. The chief are Cefn-y-bryn (548 feet) in mid-Gower, Llanmadog Hill (609 feet), the westerly extension of Cefn-y-bryn in north-west Gower, and Rhosilli Down (633 feet) in the extreme west of Gower.

This note is a record of the occurrence and character of some curious marks on a rock surface near Borth, Cardiganshire. We do not know of any previous description or reference to marks of this kind.

All of us have read how, in the infancy of modern geology, men were exceeding liberal of theorizing; indeed, it might almost be said that their theorizing, and their confidence in it, were in inverse proportion to their knowledge. Then arose the Geological Society of London, with its appeal for “new facts” and for “investigating the mineral structure of the Earth”, in other words, for application of the inductive method, and for placing geological inductions upon as broad a basis as possible. The result of which we know; the science went forward from that hour.

The Scotland Beds of Barbados have been considered as a rule to be very unfossiliferous, but Mr. A. Menzies, Geologist to the Union Oil Company, has traced at various places a thin conglomeratic band which contains fossils.

In his fair and courteous paper on the Evishanoran Esker, Tyrone, which appeared in the October issue of this Magazine (p. 451), Professor J. W. Gregory finds himself unable to accept the writer's view of the origin of this glacial feature and re-states at greater length the theory he had earlier formed. Though the area under discussion is very small—only one or two of the 4,000 sq. miles described in my paper on the Glacial Geology of the north-west of Ireland—the importance of the principles involved in this disagreement of views necessitates a reply, however brief, to the criticisms of my interpretation to which I still unrepentently adhere.

Almost all the more important teschenitic intrusions of the Edinburgh district have been examined in some detail at one time or another, but the large sill situated between Dunfermline and Charlestown is a notable exception. In the course of an investigation last autumn, the writer found, however, that, while the normal rock is not specially noteworthy, its segregations present some interesting features, particularly in view of a recent publication by Dr. G. W. Tyrrell dealing with the age and classification of the analcitic intrusions of Central Scotland.

It is quite clear that Professor Joly's presentation of his theory of basaltic cycles is, taken alone, far too simple to match the complex details of geological history. In a former paper I attempted to extend the principles he has so persuasively advocated, by adding the conception of a peridotite cycle of longer period, and I was careful to point out that even this extension led to no more than a rough approximation to the actual realities of the earth's behaviour. As soon as details are considered, the pursuit of the subject leads its explorer into a maze of difficulties, because of the many interfering factors that must also be taken into account. Nevertheless, a broad survey of the earth's history suggests that Joly has surmised what is so far the only kind of process that even begins to correspond with the dominant facts. And that, without any qualification, is a very great achievement.