The exploration of the caves in the Vale of Clwyd, and the conclusions announced by Dr. Hicks at the last meeting of the British Association, have naturally aroused much interest; for if the facts are rightly interpreted by Dr. Hicks, and the deposits which are banked up against the north-western end of the cave are really of Glacial age, then it is clear that the contents of the cave date from a time anterior to the great submergence during which those deposits were formed.

The term gneiss as generally used by geological writers signifies a rock of granitic composition in which a parallel structure in the arrangement of the constituents is more or less apparent. For our present purpose it is important to note that other plutonic rocks besides granite (e.g. diorite, gabbro, and peridotite) have their gneissose equivalents, so that, if we use the term gneiss in a structural rather than in a mineralogical sense, we may speak of diorite-gneiss, gabbro-gneiss, and so on. Now the parallel structure of gneissose rocks is of two kinds. It may consist (1) of a parallel arrangement of certain constituents (e.g. mica plates or porphyritic felspars), or (2) of an alternation of bands of varying chemical and mineralogical composition. It is agreed on all hands that a parallel structure of the first kind may be due either to the deformation of a mass of half-consolidated plutonic rock at the time of intrusion, in which case it is strictly analogous to the flow structure in many volcanic rocks, or to deformation produced by earth-stresses operating on the mass after consolidation.

The now well-known Liassic Acipenseroid fish Chondrosteus acipenseroides was named by Agassiz in 1843, but not described by him. It subsequently formed the subject of an elaborate memoir by Sir Philip Grey-Egerton, Bart., in which, besides giving a minute account of the structure of the genus, he named two additional species—C. pachyurus and C. crassior. Putting the results of Sir Philip's investigations as briefly as possible, he maintained that while “in all essential points” Chondrosteus resembled the recent Sturgeon, nevertheless in certain others, and notably in the structure of the opercular and hyoid regions, it constituted a transitional form towards the more ordinary Ganoids. Moreover, the skin of the body presented the same naked condition seen in the recent Polyodon.

In a paper recently read before the Geological Society, I ventured the conclusion that the bulk at least of the “pyromerides” of the Continent would be found to be altered lavas of an originally glassy character. The careful drawings and descriptions of various petrographers formed a strong chain of evidence; and the observations of Mr. T. Davies on materials from Bouley Bay, Jersey, seemed to establish beyond a doubt the connection between rocks authoritatively styled pyromerides and those regarded in this country as ancient rhyolites. Last autumn I visited one of the most typical continental localities, the richly-wooded Tiefenbach valley west of Wuenheim in the Vosges, and a few notes on specimens then, collected may possibly be of interest to workers in a similar field.

Under the general terms of Primary and Original, given by Werner and others, to the early crystalline rocks, have been included various mineral aggregates which may be classed under three heads: 1. The great stratiform masses of aqueous origin, essentially granitic, and formed by slow deposition at the earth's surface, which I have called Indigenous rocks. 2. Those lesser crystalline masses which were formed under similar conditions to the last, but within veins or fissures in pre-existing rocks, and may therefore be called Endogenous. 3. Rocks resembling the last in their geognostic relations, and often confounded with them, but distinguished by the fact that they have come into their present positions not by deposition from solution, but by displacement in a more or less fluid or plastic state. These Exotic or erupted masses, whether ancient or modern, are in a sense Primary, since they sustain, in one way or another, intimate relations to the more ancient rocks to which this name was first given.

The genus Piloceras was founded by J. W. Salter in 1859 upon the siphuncle of a shell closely allied to Endoceras. It was supposed by Salter that the invaginated sheaths observed in the siphuncle of Piloceras “represented the siphuncle and septa combined,” the septate part of the shell not being preserved in the specimens described by him.

At the close of the Glacial Period in North America the basin of the Red River was occupied by a large lake which has received the name of Lake Agassiz. It extended from what is now Lake Winnipeg southward for some hundreds of miles to the watershed of the Minnesota River. The bottom of this old lake now forms an extensive level plain famous for its fertility and the fine crops of wheat it produces.

The occupation of Britain by Ice-sheets in Pleistocene times has been established by the researches of Sir A. Eatnsay, Dr. J. Geikie, Messrs. Peach and Home, Tiddeman, Goodchild, and others. At the time that these inquirers made their observations, the very complex nature of the phenomena of the Greenland ice-sheet was hardly recognized, and many difficulties arose, upon which considerable light is thrown by a knowledge of the work of a modern icesheet.

The shells of Cephalopods form an evolutionary series, traceable to an ancestor unknown, but nearly related to not yet coiled forms of the Cambrian. In all descendants from this common stock homologous parts are discerned. Hence facts regarding the growth of any one form may be applied to all. Of Cephalopods with chambered shells only Nautilus, Spirula, and Sepia exist. Spirula is so rare and its shell so retrograde that no theory has yet been built on it. Examination of Nautilus gave rise to the Secretion-hypothesis, shortly stated as follows:—As the animal grows, the adherent muscles and the cincture gradually advance, the siphuncle lengthening in proportion; thus a cavity is formed between the last septum and the surface of the visceral hump: this latter then deposits calcareous matter, beginning at the sides of the shell and proceeding towards the siphuncle round which it is continued backward. During the advance of the animal the anterior portion of the mantle secretes calcareous matter, which it deposits in successive layers on the margin of the aperture (Edwards and Wood).

Among the early Tertiary Fishes in the British Museum, there are a number of detached spines and cranial fragments from the Middle and Upper Eocene beds of Bracklesham and Barton, which are undoubtedly referable to extinct members of the family of Siluridæ. With the exception, however, of three specimens figured and briefly noticed by Dixon in his work on the fossils of Sussex, all have remained hitherto undescribed; nor is it an easy task to base any satisfactory identifications upon such fragmentary materials.

So little is known of the extension through later Mesozoic deposits of Selachian teeth belonging to the familiar type of Acrodus, as represented in the Lias, that any additional evidence upon the subject is invested with considerable interest. It is impossible, of course, from these isolated relics, to determine whether the original Sharks were as closely allied as the resemblances in their dentition might at first lead one to suspect;inone case, indeed, it has been proved that the complete fish differs much from the Liassic species; but the persistence of the dental type is at any rate of some significance, and it may therefore be acceptable to offer a few notes upon the undescribed Jurassic and Cretaceous Acrodonts preserved in the British Museum. These specimens furnish evidence of at least two new specific modifications, and they are also suggestive of novel points in regard to some of those already known.

The cause, or causes, which result in the foliation of igneous rocks is a subject which at present occupies the attention of many geologists, and seems likely, in the near future, to lead to some discussion. In view of this, a short account of the foliated granite of the Himalayas may be of interest. It may be as well, however, to preface my remarks by saying that I believe that foliation may be produced in several distinct ways, and the explanation which I offer of the mode in which the foliation of the Himalayan granite has been brought about is only intended to apply to the case of that granite.

In the following pages I propose to give a brief summary only of some of the more important results worked out in detail in a series of papers published in the Eecords of the Geological Survey of India; and to add thereto a brief consideration of the question whether the foliation of the gneissose-granite of the Himalayas

In the very valuable work on “British Petrography” by my friend Mr. J. J. II. Teall, nowinprocess of publication, there is a rather full notice of an interesting serpentine which occurs in the Rauenthal (Vosges), and has been investigated by Herr Weigand. According to the latter author, as summarized by Mr. Teall,2 this serpentine “has been formed by the alteration of a hornblende rook, and the change has been accompanied by the removal of lime and the development of a chlorite, inwhich the original alumina of the hornblende is retained.”

In Decade III. Vol. II. of the GEOLOGICAL MAGAZINE, for 1885, at page 283, an abstract of a paper on “ Cone-in-Cone ” by Mr. John Young, F.G.S., of Glasgow, was given. The author of this interesting paper has kindly presented the writer with a copy of it, to which, since it was readinGlasgow last year, has been added some additional remarks, together with two very beautiful plates, by ‘ photogravure,’inillustration of some of his typical Scottish specimens.

I have had occasion lately to thoroughly investigate these and other allied Ammonites, partly because it has been important to me that I should know the true affinities of these species, partly because my attention was directed to certain still obscure points with regard to their identification, and partly on account of the statement by the late Dr. Wright that Am. serpentinus and Am. falcifer were the same species. In pursuing my investigations I have received a great deal of assistance from Dr. E. Hang's Beiträge zu einer Monographie der Ammoniten-gattung Harpoceras, which I am pleased to acknowledge, although I do not find myself able to agree with him in one or two small points which I will presently mention. Meanwhile, by the aid of a few references to well-known works, I will indicate the Ammonites so that they may be understood.

Description.—Shell conical, turrited; apex acute; spiral angle regular, whorls 8–9, angularly carinated anteriorly; sutures wide and deep; each whorl bears 3 spiral rows of equally spaced but unequal neatly rounded tubercles; the anterior of these, which are much the largest, are set on the carina; the middle row consists of fine granules, whilst the nodules of the posterior row, which adjoin the posterior suture, are intermediate in size and half-way between the other two. Fine, close-set curved striæ of growth cross the whorls transversely, but are scarcely discernible even with a lens, except on the last whorl of well-preserved specimens.

During a recent examination of the lead-mines of Derbyshire, I was interested in some accounts of explosions which had taken place, which were not due either to any material used by the workmen or to fire-damp. Though at first inclined to believe that the accounts were exaggerated, I soon found that not only was the evidence of such explosions having constituted a real danger to the men overwhelming, but that accidents are still liable to occur from this cause. The explosions are connected with the structure known as slickenside in the veins.

The accumulations of drift in the vicinity of the town of Sudbury have been described by Mr. Whitaker in the Geological Survey Memoir upon the N.W. part of Essex and N.E. part of Herts, etc.; and additional notes are given by the same author in the Memoir upon the Geology of Ipswich, etc. Since the appearance of these memoirs the sections have altered considerably, and one of the exposures is of such interest, that a record of it seems to me desirable, as in a few years it will be doubtless destroyed, and one more link in the chain of facts which have to be considered in attempting to account for the mode of formation of these drifts will have disappeared.

The specimen under notice is relatively shorter, broader (higher), more triangular, and with sharper ridges than the figure in the ‘Monograph,’ 1856, pl. vii. f. 21. The anterior hinge is more prominent, and the front margin rather oblique. It is also narrower behind, ending with three small spines or denticles. The edge viewis acute-ovate. From the Belosepia-bed, Bracklesham. T. R. Jones’ Collection.

The two admirable summaries of our knowledge of fossil Crocodilia recently published by Mr. A. Smith Woodward—the one relating to British forms, in this Magazine, and the other, comprising the whole order, in the “Proceedings of the Geologists' Association”—render it a comparatively easy matter to find out what is known concerning any particular species or genus; and I may accordingly at once proceed to the proper subject of this paper.