Splitting, crushing and spalling which occur when boulders move against each other, generate fine material and so give rise to angular large and small sizes. The nature of the rounding process can be deduced from the analysis of moments of the roundness frequency distribution of the size range 4–128 mm. A low standard deviation indicates the dominance of one process—either abrasion or breakdown; a high standard deviation indicates the presence of both. The relationship between mean roundness, standard deviation of roundness, skewness of roundness and mean size allows for an analysis of the size reduction processes at work on the sediment; and for a comparison between the reactions of different rocks. A model, based on actual data, is given for the evolution of roundness of limestone clasts on a beach.

During the past year several igneous erratic boulders have been noticed on the cliffs of South Pembrokeshire by Mr. A. L. Leach and myself, in situations where no such erratics were previously known, so that a record of the larger ones seems advisable; five of them being dealt with in the following paper. At Mewsford Point, near St. Govan's Head, there is a well-rounded boulder measuring 4 ft. 1 in. × 2 ft. 6 in. and about 2ft. 6in. high, weighing approximately 32 cwt., and visible from some distance because its outline and dark colour differ markedly from the surrounding crags of Carboniferous Limestone. It appears to be the southernmost igneous erratic boulder in Pembrokeshire, and hence is of more than usual interest.

On page 320, in the fourth column, the first three lines should not read as printed with the brace, but as follows:

Overlying Zone of Ammonites planorbis.

Kössener Schichten and Dachstein Series.

‘Hauptdolomit’ of Tyrol, and ‘Plattenkalk’.

In my former note on the discovery of Bos primigenius in the Lower Boulder-clay, I stated that there was some “slight twisting and confusion” of the stratified deposits below the superincumbent Boulder-clay, which might have been caused by the pressure of glacier-ice. As the crumpling of sandi clay, and gravel, below Till, is by no means uncommon, and has frequently been described, I did not think it worth while at the time to give any drawing of the contortions exposed in the new railway cutting. But some geological friends having asked me about the character of these crumplings, it may not be out of place if I now add a few particulars. "When my former note was written the disturbed portions of the stratified deposits were not very well exposed, and consequently I did not in my communication lay much stress upon their occurrence, although I had little doubt as to their origin. Upon visiting the section some weeks later, however, I found the crumplings well displayed. In October last I saw them again, in company with my brother, Mr. A. Geikie. By that time the section had been still better developed, and the annexed sketch of a portion of the crumpled clays was made.

The requirements of towns, and even of camps, in the matter of water supply are so great nowadays that surface waters are avoided as likely to be contaminated, and there is consequently a great desire to rely on deeper sources. Quite an official literature has sprung up of late years, and important memoirs have been issued by the Geological Survey on the “underground sources” of several counties. So far as I am aware there has been no official memoir relating to the county of Dorset, and this probably arises from the circumstance that the artesian principle has not been made use of to any great extent until recently, although the Dorset syncline would seem to bo eminently suitable for artesian wells.

Of this remarkable genus several species from the Lower Silurian rocks of Russia have been well described and illustrated by Eichwald, Pander, de Verneuil, Kutorga, and others, to whose works and papers the reader is referred.

In my brief paper published in this Magazine for 1880 (Decade II. Vol. VII. p. 404), I mentioned that pebbles of felstone were not uncommon in the Bunter conglomerate on the northern part of Cannock Chase. Since that time, as opportunity has occurred, I have been making a more special study of these pebbles, and think it may be worth while publishing a description of some of the commoner varieties, as a contribution to the lithology of this interesting deposit and a help to the determination of the question of the origin of its material. I believe that I have observed most of the varieties, which commonly occur in the district, but do not pretend (for circumstances have not allowed of this) to have made anything like a complete collection. Many of my specimens have been derived from the broken materials spread upon some roads newly made over the portion of the Chase in the vicinity of Rugeley, but several of them were obtained in a large pit in the Bunter itself, by the side of the railway on the road to Hednesford, and I was able by a careful search in it to identify most of the varieties that I had collected elsewhere. I cannot say that erratics are absolutely unknown in this district, but they are extremely rare, and there is practically no danger of making a mistake as to the source of the pebbles. These pebbles of felstone (to use an inclusive term) appear to be by no means rare. I think one could hardly search a couple of square yards of a newly “metalled” road without picking up a fragment. Now and then specimens are found with a dark ground-mass, and occasionally one which seems to be an indurated felspathic breccia; but in the majority there is a certain common character, though there are many varietal differences. These have a compact ground-mass, varying from a pale brick-red (the commonest) to some tint of pinkish-grey.

The next operculated species which claims our attention is the Calceola Gotlandica of F. Roemer. This species has been removed from the class Brachiopoda in a list of the Upper Silurian Brachiopods which I published in 1860. I now give my reasons for so doing (then but briefly indicated).