Since the advent, in 1840, of Sir Win. Logan's paper “On the Characters of the Beds of Clay immediately below the Coal Seams of South Wales,” underclays have generally been regarded as representing the soils on which grew the vegetation now forming the coal. I am not aware, however, that any definite and detailed hypothesis has been put forward to account for their origin. The superior interest attaching to the question of the origin of coal has apparently overshadowed the less important underclay, and it has been left to fit itself in with any particular hypothesis of the former which happened to be in favour. At the same time, two general views of its origin have been suggested which do not, however, go into any detail as to the exact manner in which it has been brought about.

In the south-west of the Lleyn peninsula, the country inland is generally covered by drift, but the Survey map marks some isolated patches of rock as “Serpentine.” When I first visited the district, with the kind encouragement of Professor Bonney, under whom I was continuing my work at University College, I made a collection of these so-called “Serpentines” from ten different localities. The one at Porth din lleyn had been shown by Professor Bonney to be mainly diabase, and others of the examples have been since described in a previous number of this Magazine and elsewhere, but we have yet no complete account. I have, therefore, attempted to give a short summary, as preliminary to some discussion of the district.

The most exclusive advocates of the hypothesis of the terrestrial origin of Coal admit that those small irregular patches, veins, and nests of the same occurring in beds of sandstone are formed of drift vegetation. And admitting this, it is difficult to draw the line until we have ascribed a similar origin to certain definite coal seams of considerable extent. Granting this much, however, is obviously a different thing from the belief that all coal seams are to be ascribed to drift vegetation; and while the following remarks are intended to show what a strong argument such drift coal in sandstone furnishes for the probable drift origin of certain coals, there is no intention of ascribing such an origin to coal in general.

In a review of Nicholson's “Geology of Cumberland and Westmoreland,” which appeared in the GEOLOGICAL MAGAZINE about a quarter of a century ago, the reviewer observes, in referring to some remarks upon the Shap Granite, that this and other granites have clearly taken the place of the rocks whose position they occupy, and that, in fact, intrusive rocks can be shown, in a great majority of instances, to have replaced, rather than to have displaced, the rock masses which they invade. The reviewer's identity with a wellknown Professor of Geology at one of the English Universities is sufficiently evidenced by his intimate acquaintance with the geology of British Silurian and Cambrian rocks.

Geological opinion is still divided on the subject of the formation of the Boulder-clay. By some it is held to be the sole work of the ice, and accumulated beneath it; by others it is looked upon as a marine deposit, though deriving its materials from the grinding action of the ice-sheet or glacier. Some geologists, again, hold that the “Till”—as distinct from the Boulder-clay— was formed beneath the ice, but that the latter is a marine deposit laid down in glacial seas.

The existence of rocks possessing, when the laminæ are not too thick, the property of flexibility has long been known. Upon flexible sandstone (“Itacolumite”) a great deal has been written at different times, and of late years important work has been done which renders it necessary to greatly modify the opinions formerly held with regard to this rock. Notwithstanding the interest which, is attached to the subject, it is one very much neglected by our textbooks, the British, either ignoring it altogether, or treating it with the utmost brevity, the German, while sometimes referring to it at considerable length, do not do more than enunciate the old views. To Prof. Judd—who has kindly aided me with advice, and by affording facilities for preparing this paper—I owe the suggestion that it would therefore be useful to give a résumé of the present state of our knowledge upon the flexibility of rocks in general.

In the Geological Magazine (Dec. III. Vol. VIII. No. 329, p. 493, Nov. 1891), Mr. E. T. Newton has a “Note on the Occurrence of Am. jurensis in the Ironstone of the Northampton Sands in the Neighbourhood of Northampton.” This note had especial interest for me, from my having contested Mr. Beeby Thompson's view of the Jurensis-zone being represented by the clayey beds beneath the Sands; and, in fact, it seemed to support my argument. Further reading, however, obliged me to confess that I could not claim this support; for Mr. Newton says (p. 494), “that the specimens of Am. jurensis agree exactly with Dr. Wright's plate 79 (Lias Ammonites).”

Mr. Mellard Reade's book on the “Origin of Mountain Ranges” has now been before the geological public for five years; it has been reviewed in this Magazine and elsewhere, and several more or less weighty objections to the theory have been put forward; but no very complete examination of it has been attempted. This may be partly due to the manner in which Mr. Reade has presented his theory, for he has certainly been too diffuse over points which require very slight illustration and not nearly explanatory enough on other points of great physical difficulty.

I Have obtained a considerable number of specimens of Thecidium ornatum, Moore, from the Coral Rag, in the bed containing Phasianella (Pseudomelania) striata; Pseudodiadema versipora, Hemicidaris intermedia, etc., from a quarry between Ayton and Scarborough. My friend, the late Mr. Charles Moore, F.G.S., gave me some specimens of this Brachiopod from the Coral Eag of Lyneham, Wiltshire, with which the Yorkshire Thecidium perfectly agrees in form. This shell, especially the dorsal valve, is plentiful at Ayton, but it is troublesome to find on account of its small size; it is best obtained by washing the marl; occasionally it is found attached to Ostrea.

Taking the other and coarser constituents of such slates as are X not wholly made up of the fine “base,”—the constituents which may be spoken of as “porphyritic,”—the lapilli vary very greatly in number and distinctness. In a large part of the roofing-slates they are either no longer discernible at all or are so exceedingly faded and blurred as to be just barely recognizable, often as patches altered to chlorite, or chlorite and calcite, in which the felspar-laths of the original andesitic ground-mass may still be seen comparatively little altered. In cases where there is reason to suppose that the lapilli were largely of more basic nature, this almost complete alteration of them is observed, as might naturally be expected.

Whilst studying the sedimentary roofing-slates of North Wales and Cornwall, and allied materials, my attention was also directed to those most interesting rocks, the ash-slates of the Lake District, often externally so closely resembling some of the Welsh and Cornish examples, though differing so much in origin. In course of time I have collected, and had sections prepared from, a considerable number of specimens from many quarries and other places at various parts of the district, both very fine-grained wellcleaved actual roofing-slates and also the attendant coarser beds.

In the course of my work in the Highlands of Forfar, I have been much struck with the mode of occurrence of certain light-coloured gneisses, of undoubted igneous origin.

They are intruded into the surrounding rocks in an infinite number of thin bands or sills, generally interlacing, and often not more than two feet thick; sometimes not exceeding an inch. Their bulk in some areas exceeds considerably that of the older rocks, at other times it is far less.

Two points are easily noted; first, they have no selvage edge; secondly, they have a very characteristic aspect, due to rounded grains of oligoclase.

In “The Cause of an Ice Age” Sir R. Ball claims to have removed from the Astronomical Theory of Glaciation the greatest stumbling block in the way of its general acceptance, and to have placed it on a firm and unassailable foundation. And this stumbling block he considers to have been Sir J. Herschel's erroneous statement, that, of the total heat received by a hemisphere in a year, one-half is received during the summer, and the other half dining winter.

The vexed question of the affinities of the fossil organisms known as Xanthidia—a question which only experienced zoologists and botanists can hope to solve—will not be discussed in this short paper, my intention being merely to show that these interesting organisms are not confined (in England) to the Chalk flints and Grey Chalk, but exist in the London Clay, and to give a short account of the means of isolation and of the appearance of these minute fossils.

While engaged in the examination of the superficial deposits of the Maltese Islands, I have often met with rounded pebbles and angular fragments of a black, crystalline limestone, either lying on the rock surfaces, or embedded in the Quaternary formations.

The late Professor Leith Adams drew attention to the same fact as long ago as 1867, and in a paper which was published in the Quart. Journ. Geol. Soc. he expressed an opinion that the fragments which he had seen lying on the surfaces of the sides and summits of the Gozitan Hills, belonged to a formation that was of a much later age than any of the rocks that are now to be found in situ in the islands.

Dr. John Murray, too, notes in his brochure on the Maltese Islands the occurrence of similar fragments in the neighbourhood of Marsa Scirocco, and he further adds that no evidences of the rock having been found in situ in the islands had hitherto been recorded. The remarks of these gentlemen led me to consider the matter attentively, and I have, during the last year, been carrying on investigations with the object of discovering the origin of the black marble, the result of which has been to show that it is but a variety of the Lower Coralline Limestone, the basement bed of the Maltese series, and that it occurs extensively in situ in that formation.

Over twenty years ago I commenced the study of the glacial deposits of the neighbourhood of Liverpool, and as the observations grew they came to embrace a considerable share of the drainagebasin of the Irish Sea.

I have personally inspected and kept full records of all of the important artificial excavations likely to throw light upon the subject, in addition to examining and making sections of the natural exposures of glacial drift which abound on the north-west coast of England, the coast of Wales, and in the river valleys draining into the Irish Sea, and to a lesser extent the drift on the east-coast of Ireland and the south of Scotland.

The recent contribution of Mr. Reade to Glacial Geology (GEOL. MAG. July, 1892, p. 310, et seq.) is a challenge which I take up in default of a worthier champion.