The main thesis of this paper is to show that the Ludlow Bone-bed forms the true base of the Devonian System. This is urged on several grounds.

(a) Priority. It was the limit originally used by Murchison. Although subsequently altered by him, one finds if one attempts to use his later limit:—

(i) That the Old Red Sandstone was not re-defined accordingly.

(ii) That Dumont's Rhénan (Devonian) System, defined in 1845, has priority over Murchison's later definition (1848).

(iii) That the later limit adopted by Murchison does not form a true horizon and has been very differently interpreted by later writers.

(b) Palæontology.

(i) There is a marked faunal change at the Ludlow Bone-bed. The Bone-bed marks the first appearance of fossil fishes, and thus the Devonian marks the dawn of an age of vertebrates. There is only one old record of a pre-Devonian fish in the British Isles; one doubtful one in Gotland, and an anomalous one in the Ordovician of America. The Shropshire succession forms a standard of comparison for all areas of the Old Red Sandstone type of deposit.

(ii) The limit adopted after a detailed study by other writers of an uninterrupted marine series is on the same horizon. The succession at Liévin (Northern France) forms a standard for comparison of all areas of the Devonian (marine) type of deposit.

(c) Stratigraphical. In England the Ludlow Bone-bed marks also a change in physical conditions, more noticeable elsewhere as an unconformity. Physical breaks or unconformities on the same horizon occur in Scotland, Belgium, Brittany (slight), Norway, Sweden, and Spitsbergen.

(d) Practical Considerations. The Downtonian rocks, i.e. the strata from the Ludlow Bone-bed horizon upwards, form a stratigraphical and palæontological entity, incapable of broad or even of rough separation below the Dittonian. The Ludlow Bone-bed, on the other hand, forms an horizon which can be recognized and mapped all over North-Western Europe. In England there appears to be a slight faunal break between the Downtonian and Dittonian, but this is less marked elsewhere.

Fifty years ago, when Professor Seeley gave his masterly description of the Dinosaurs of the Cambridge Greensand, so little was known of these animals that it was naturally impossible to co-ordinate the different remains and to fix their systematic position. Up to 1902 scarcely any attempt was made to review Professor Seeley's conclusions. In that year I tried myself, in a paper, to determine their systematic position, but I find I was mistaken in some points. In 1917 Mr. Bajazid Elmas discovered at Szentpéterfalva some remains of Struthiosaurus that throw much fresh light on the position of this genus, and thus also on the allied genus Acanthopholis. Owing to the war the utilization of these discoveries had to be postponed, but now an attempt can again be made to group the Dinosaurs of the Cambridge Greensand.

Nearly a hundred years ago the limestones in the Chapelton district of Jamaica were recognized by Sir H. de la Beche as being of the age of the Calcaire Grossier or the London Clay through the finding in them of a gigantic Cerithium whose cast resembled that of C. cornucopiae Sow. De la Beche does not employ the term. Yellow Limestone in his table of the Jamaican rocks, but he refers to beds of yellowish limestone as forming the base of the White Limestone. The term Yellow Limestone came into use at the later period of the survey under Barrett and Sawkins.

The exact and exhaustive study of the Quaternary terraces of the Somme, which we owe to Commont, may well serve as a starting point in any consideration of this subject. In its results it is not without its surprises, for we should scarcely expect to find, as we do, that the gravels which form the earliest deposits on each of the three lower terraces all contain the remains of a “warm” fauna; the third or highest of these terraces affording Elephas meridionalis, the first and second E. antiquus and its companion Hippopotamus. Associated with these faunas are flint implements of early types. Pre-Chelléan in the third terrace, typical Chelléan in the second, and Chelléan “evolué” in the first. No signs of a cold climate are to be discovered in any of these gravels until we reach that of the first terrace, where a newer gravel is to be seen invading the older and bringing with it Acheuléan implements and the mammoth.

The occurrences herein described have been brought to light as a result of the work of the Road Materials Division of the Geological Survey of Canada. Those at Ste. Monique and at Husereau's Farm, near Oka, were discovered by Mr. H. Gauthier in 1916 (1), and those at Isle Cadieux, Como and Cascades Point were discovered by Mr. R. H. Picher in the same year (2). It is owing to the kindness and courtesy of Mr. William McInnes, at that time directing geologist of the Geological Survey of Canada, and of Dr. L. Reinecke, at that time chief of the Road Materials Division of the Geological Survey of Canada, that the writer has been given the opportunity of studying these rocks.

In the Transactions of the Edinburgh Geological Society (vol. x, 1912, p. 49, pl. v, f. 8) I gave a figure of an Ichthyocrinid which occurred in No. 1 Bed, Invertiel, along with other members of the family, all of which were referred to ? Forbesiocrinus. In the spring of 1913 I had the pleasure of sending my specimens of flexible crinoids to the eminent crinoid authority, Dr. Frank Springer, of the United States Museum, Washington, who was then engaged on a comprehensive study of the group. For some reason or other I did not forward this particular specimen, probably because I did not think it well enough preserved (No. 939, Fig. 3 of present paper). The other Ichthyocrinids from Invertiel were referred by Springer to his new species Amphicrinus scoticus. It so happens that No. 939 was the only specimen of its kind which I had at that time cleaned and mounted in my collection, although as the sequel will show it is evident that I had found several others in the field, but had erroneously laid them aside as Amphicrinus scoticus. This is a mistake which could easily be made, since I was not then fully aware of the special characters which distinguished A. scoticus.

1. Inselberge, which form striking features in the landscape of most of tropical Africa, have attracted the attention of many writers, and various theories have been advanced to explain their formation. Passarge (I) considered that desert conditions are the most favourable for their maintenance, as wind scour was believed to be a potent factor in the deepening of the hollows between them. Bornhardt (2) and Falconer (3) suggest that they may result from repeated cycles of pluvial erosion, due to normal crustal oscillations, and with this view Theile and Wilson agree (4). From a study of the inselberge in Nigeria, the writer will endeavour to show that the climate of the Sudan, with its alternate wet and dry seasons, is favourable to the production of inselberg landscape.

The remarkable specimen dealt with in this paper was discovered by Mr. R. May, of Downing College, Cambridge, in the earlier part of the year 1922, and was forwarded to me by Mr. Henry Woods, F.R.S., for study and description. Mr. Woods informs me that “the specimen was found in the Boulder Clay of Hertfordshire, and consists of a portion of a body-chamber of a Perisphinctoid Ammonite in the matrix of which there are wings of a dragon-fly. The ammonite is, of course, derived. It has been examined by Dr. L. F. Spath, Dr. F. L. Kitchin, and Mr. J. Pringle, each of whom has stated that he believes it has come from the Ampthill Clay (of Corallian age)”.

There is a tiny but very interesting inlier of Upper Ludlovian and Lower Downtonian rocks at Saltwells, near Stourbridge. It has been described in detail by Messrs. W. W. King and W. J. Lewis, and will not be redescribed here.

To the old volcanoes of East Fife Sir Archibald Geikie assigned a Permian age. In the course of a characteristically able series of investigations he discerned that on the shore at Lundin Links one vent had penetrated some of the highest members of the Scottish Coal Measures, whereas at Kennoway another could be seen to have risen through the Millstone Grit. There further appeared to be a general similarity in the lithologic and petrographic characters of the materials of the entire group, thus linking them together, and they seemed to have taken birth after the inception of the tectonic features of the area. Only one simple conclusion emerged from a consideration of these facts, namely, that the vents must be referable to some period of post-Carboniferous time. In support of that opinion he pointed especially to the Largo district, where he thought he could detect a sheet of fragmental volcanic material resting with a distinct unconformability upon the folded and denuded Carboniferous strata, which supposition, of course, could it be confirmed, would render further discussion upon the matter unnecessary. But in the East Fife Memoir it is stated that the sections which might be expected to furnish critical evidence are not clear.

The High Plateau is a rather ill-defined region occupying the south-eastern portion of Brazil. It rises abruptly from the south-east coast but slopes off very gradually to the north and west. In consequence the rivers flowing north and west are of great length and importance in navigation. Those flowing south are useless for navigation though of great importance for water power. An interesting exceptional river is the Parahyba flowing east and parallel to the south-east coast-line curve. The geology of the whole region is essentially granite and gneiss with curiously metamorphosed quartzites and schists. The accompanying map was made by the writer during some explorations carried out over this region in 1919, and as some of the points studied and already published (1), (2) were new and surprising to geological science, the following general description is added.

The system magnesia-alumina-silica is one of great importance in petrology, and the paragenesis of its constituent minerals must be a subject of study in any enquiry into the thermal metamorphism of rocks which have these three components as important constituents. Such rocks include particularly those of argillaceous type, magnesian-carbonate sediments, and bauxitic rocks.

Rhombic pyroxene as a constituent of thermally altered sediments has hitherto been recorded only from a few contact zones, and, as the conditions under which it is generated in metamorphosed sediments are of some interest, these may be examined.

In 1902 the author proposed a new classification of the genus Lichas, introducing several new subgeneric names. Gürich's valuable paper dealing with the same subject, which was published late in 1901, unfortunately only came into his hands after his article was in the press, so that full justice could not be done to it. Since that time a considerable amount of work has been done on the genus Lichas, but the principles governing the classification put forward in 1902 have not been upset, and no fundamental modifications have been introduced, though many new species have been described and several new subgeneric or generic divisions have been established.

A boring that was completed in 1921 by Messrs. Pease and Partners, at Roddymoor Colliery, near Crook, Co. Durham, about 5 miles north-west of Bishop Auckland, is of considerable importance. I had the good fortune to be consulted in connexion with the correlation of the strata in the lower part of the section, and was also allowed to make a thorough examination of the whole of the cores. The stratigraphical results are of much interest, and it is mainly with these I propose to deal in this paper. Mr. R. G. Carruthers, of H.M. Geological Survey, also examined the cores, and on his suggestion they were broken up and the fossils in them collected by Mr. Tate, of the Survey. It is hoped that when these are determined, results may be obtained which will aid the zonal classification and correlation of the Lower Carboniferous rocks of the two north-eastern counties.