Aggradation of the bed of a river is a well-known and common phenomenon in certain circumstances, but in the present case a mountain stream, whose grade is to steep that waterfall are present, is found flowing along the top of a well-marked but very irregular ridge to tufa. This is found in a little stream near the village of Binn, known to mineralogists for the rare minerals which occur in metamorphosed Triassic dolomite not far away up the valley of the Binna.

In a paper (1) by one of us (W. F. F.) reference is made to the occurence in Midland sediments of apatite grains having dark purplish, often pleochroic, cores or nuclei. From an examination of the heavy minerals in Midland rocks ranging from Cambrian to Trias it is evident that these peculiar apatite grains occur at several horizons. Discoloured grains appear in the Cambrian quartzite and apatite of smoky tint in the Old Red Sandstone. In the Carboniferous rocks, dark-banded grains varying in tint from yellowish-brown to smoky-purple and occasionally pleochroic, occur with fair frequency. Similar grains are particularly noticeable in the Gornal Sandstone, which lies in the lower part of the Middle Coal Measures of South Staffordshire. An hexagonal cross section of apatite from this rock, with a dark core, was figured in the paper referred to above. Similar grains occur, though rarely, in the Enville and Bunter Sandstone, but increase in frequency in the lower Keuper Sandstone. The dark-colored “cores” may be sharp-edged or rather indefinite in contour, narrow or broad, and variable as regards depth of tint. Clear-cut bands or stripes of dark colour are exceptional.

The Plate which accompanies this article, showing till over-riding and overthrusting in its readvance the gravels on which the yard of Harvard University is built, is of a temporary exposure. This was made in putting in a large apartment house at the north-west corner of Arlington Street and Massachusetts Avenue, North Cambridge. The camera was pointed north. Realizing its ususal character, I got my colleague, Prefessor M. S. Munro, who is a virtuoso with the camera, to take it, and have used it as a postcard to friends. One of them, my old teacher, William Morris Davis, said it was unexcelled, and urged its publication. That is the occasion of this article, for, when I came to think of it, to obtain such a photograph required an unusual combination of circumstances:—

(1) The artificial excavation;

(2) A strike that suspended work at the critical time (it is an ill wind that blows no one good);

(3) Just such conditions of wind and drying out as to bring out the different beds in the sands. The coarser ones dry and crumble more rapidly, while the fine hold the dampness and stand out. We might add:—

(4) A man living on the street (myself) to appreciate it, and

(5) A friend who is an excellent photographer.

From the southern shores of Dublin Bay there stretches to the south-west a broad granite intrusion with rocks of supposed Ordovician age on both sides of it. These rocks are metamorphosed near the granite, and the belt of metamorphism is wider on the south-east than on the north-west side, indicating, no doubt, that the plane of junction dips more steeply on the latter side. Near Dublin the Lower Carboniferous rocks rest unaltered upon the granite. On the south-east side, in the northern part of the county of Wicklow, the belt of Ordovician rocks is only some 2 miles wide, and a large area of supposed Cambrian rocks lies between it and the sea. Around the hill of Carrickgollogan a. patch of similar rocks appears incongruously in the middle of the Ordovician belt. After a study of the region to the south of Dublin one seems to be naturally drawn towards this small area around Carrickgollogan, for it presents a problem, the key to which may explain the geological structure of a much wider area.

Having always been much interested in any evidence that might throw light on the relationship of early man to the glacial drifts, I have for twenty-five years or more watched the various beds of gravel that occur above, among, and below the Boulder Clays in the north-eastern counties for anything resembling a Palaeolithic implement. I had no approach to success, however, till about a year ago, when in a bed of water-deposited gravel at a place called Limekiln Gill on the Durham coast, between the entrance of Hesleden Dene and Blackhall Rocks, some 4 miles northwest of Hartlepool, I found in the gravel cliff about 4 feet above the level of the beach a piece of yellow quartzite, which seemed to be artificially chipped. A short while ago I sent the specimen to Mr. Reginald A. Smith, B.A., F.S.A., of the British Museum, for his opinion, and somewhat to my surprise received the following reply: “I have little doubt about your implement, and Mr. Reid Moir, who saw it yesterday, agrees that it is definitely human. It is, indeed, interesting to find such a thing in situ, and one might expect to find it in some margin between the two principal boulder clays (Interglacial of East Anglia).” Such being the opinion of these experts, the specimen becomes one of very considerable significance, since the bed in which it was found underlies the main Cheviot and Northern drift or Purple clay, which at this spot is at least 70 feet thick and consists very largely of typical boulder clay.

F. P. Paul described in 1906 (T.M.P.M., vol. 25, p. 309) a nepheline-eudialite-basalt from Shannon Tier, Tasmania, containing an unknown mineral referred by him to Ca2SiO4. Subsequently Bowen (Amer. J. Sci., 1922, p. 30) pointed out the close correspondence between the optical properties of Paul's mineral and of the artificial βCa2SiO4 prepared by Day, Shepherd and Wright. Still later (Geol. Mag., 1927, p. 43) the writer of this note ventured to apply the name shannonite to the mineral of this singular occurrence. Since that time through the kindness of Mr. P. B. Nye, Government Geologist of Tasmania, a specimen of the rock described by Paul from Shannon Tier has been obtained and examined. That the specimen examined is identical with the rock described by Paul is clearly indicated by his detailed description and the photomicrograph which accompanies his paper. Unfortunately my own determinations are not in agreement with those of Paul, and the purpose of the present note isto state the nature of these discrepancies. The rock is a felspar-free nepheline-basalt of which the chief constituents are idiomorphic nepheline, a titaniferous augite, olivine (chrysolite), the unknown mineral of Paul, biotite, apatite, magnetite, perofskite, and minor amounts of interstitial analcime. The described eudialite has not been discovered, and from the description attached to the photomicrograph this mineral appears to have been confused with nepheline. I find further that the properties of the unknown mineral agree, not with those of any of the artificial calcium orthosilicates, but with those of monticellite. The two olivines are readily distinguished in thin section, the chrysolite occurring as chadacrysts and the monticellite as oikocrysts, the latter appearing as shapeless grains often surrounding chrysolite and enclosing numerous idiomorphic crystals of nepheline and magnetite, and thus belonging to a late stage in the crystallization history of the rock. The chrysolite moreover is readily distinguished—apart from these textural differences—by its higher birefringence and larger optic axial angle (near 90°).