are has been indicated on Fig. 2, on which are plotted diagrammatically what may be called the ramparts of Paris.

The first point is that the rocks of the Basin and its margins are geologically younger as one proceeds from east to west. Triassic beds-the oldest of the Secondary rocks-form that continuation of the High Vosges which northwards expands into the Hardt region, itself topographically, though not geologically, continuous with the Rhine Highlands. On the other hand Paris, like London, lies in a Tertiary basin. Between these two extremes we have successively Jurassic (oolitic) and Cretaceous (chalk) beds. All these beds are geologically young, all are relatively soft. They never form lofty or continuous uplands. But and this is the important point-they are not uniformly soft. Softer beds often alternate with harder ones, and where there is a marked difference in consistency between two adjacent beds, the softer rocks tend to be worn out by rivers and thus to form valleys, above which the harder beds rise in escarpments. Parts of the courses of the Moselle and the Meuse, the peculiar east-to-west line followed by the Seine during a short tract, are all alike determined by the outcrop of easily eroded beds, and in each case therefore a scarp, or steep-sided hill, bounds one side of the river valley.

The more important of the scarps so produced are indicated in a quite general fashion on the sketch-map, and their significance is perhaps best realised by naming the towns which mark their course. Almost all these scarp towns will be found to have played an important part in the present war, and thus to have become household words for thousands here.

Paris, as already stated, lies in an area composed of Tertiary rocks. These are harder than the Cretaceous clays, etc., which form the next aureole to the east, and thus the margin of the Tertiary zone is marked by an eastward-facing scarp, marked I on the map, through which the rivers cut their way. The position of the towns of Laon and Reims near this scarp is important.

The next ring consists of chalk, but this chalk is generally soft, and the sharp alternation of beds of different character, necessary to produce a definite scarp, is usually absent. Only in the case of the Argonne, a low forested upland, is there anything in the way of a distinctly defined elevation, and this over only a short longitudinal distance. As we approach the Meuse we pass from Cretaceous to Jurassic beds, and these show a very sharp alternation, generally of hard limestones with soft calcareous beds or clays, the first giving rise to definite scarps. Two of these are noticeable and are indicated on the sketch-map. One occurs in the vicinity of the Meuse river (II on map). Immediately to the east of the fortified town of Verdun the outcrop of hard limestones is well marked, forming the Côtes or Heights of the Meuse, which played so important a part in the Verdun fighting. St. Mihiel, which has also appeared in many bulletins, is another scarp town, lying to the south of Verdun.

The Moselle, for a part of its course, runs in the soft Lias clays which mark the base of the Jurassic series. Westwards of these soft clays a bed of hard limestone crops out, and forms, to the west of Metz, another important scarp, the Côtes of the Moselle (III on map). That at the base of this scarp rich iron-containing beds occur adds, as we shall see, a new complication to the Alsace-Lorraine problem. The scarp towns here are numerous; we would emphasise Metz, lying in the plain at the base of the limestone hills, and Nancy; both are strongly fortified.

East of the Lias clays we come to the Upper Trias beds, chiefly marls, like those which floor much of Cheshire, and, like those, saltbearing. These underlie the high plain or plateau of Lorraine. Farther east appear the Lower Trias beds, mostly grits and sandstones, harder therefore than the marls, and forming higher ground. These grits are, as it were, plastered on the sides of the High Vosges; in reality they have been removed from the summit levels by erosion, but we speak here of appearances only. Further, they continue the chain of the High Vosges into the Low Vosges, which expand in breadth and rise in height as they pass north-eastwards into the Hardt. Crystalline Vosges, continued into the grits of the Low Vosges and the Hardt, may be said therefore to form the fourth rampart of Paris to the east, though their structure and origin are different from that of the scarps which we have described as forming the other three ramparts.

On the sketch-map a pass is marked as the Col de Saverne. Saverne is of course the Zabern of the Germans, and the name and its significance should be carefully noted. Broadly speaking we may say that the Saverne pass lies near the end of the Crystalline Vosges. It is the region where the elevated forested belt which stretches from the High Vosges to the Hardt is lowest and narrowest Strasburg, on the Ill, lies almost directly east of Nancy, on the Meurthe, a tributary of the Moselle; the Col de Saverne is the natural line of communication between the two; between what was till 1871 French Alsace and France proper; between the present German Reichsland and France. Here runs the great main railway route to Paris vid Nancy, here the canal which connects the Marne and the Rhine; here also, in conquered land, on a highway of invasion, German officers gave the world before the war an exhibition of Deutsche Kultur.

Let us briefly connect these facts with the events of the war.

Why did the Germans adopt as their main line of invasion in 1914 the valley line following the north-western margin of the Rhine Highlands, the line which follows the course of the Meuse, then that of its tributary the Sambre, and is continued into the Oise valley? Because thus, and thus only, could they turn all the four ramparts of Paris. Why, in 1871, did they establish themselves at Metz and beyond? For more than one reason, as we shall see, but among others because they were thus able to seize the outermost rampart at the point where it was most widely breached, and the next rampart at its most important point. Their purpose was definitely aggressive, not defensive. Note also the chief incidents of their offensive during the present Their treachery in invading Belgium seemed at first to pay, for von Kluck in September 1914 was within reach of Paris, and had evaded all its fortified lines. The battle of the Marne has often been described as a miracle; even the geographer may be excused for saying that it suggests that might lies not only in the sword and in the fort, but in something deeper. Turned back from Paris, the German armies established themselves on the Aisne, and to-day still hold Laon, on the edge of the westernmost barrier. The Argonne played its part in the battle of the Marne, despite its relative insignificance. On September 8, 1914, the Chief War Lord stood waiting, wrapped in his martial cloak, we are told, to make that triumphant entry into Nancy which was to mark the conquest of the continuation of the rampart which runs north and south from Metz. That triumphant entry has been indefinitely postponed. The siege of Verdun was in part an attempt, due to the failure of the first offensive, to make that direct western attack on Paris from which the German staff shrank in August 1914.

Summary as these notes are, they may serve to suggest the strategic value of the moderate elevations which guard Paris from the east, and are themselves due to differential erosion in the rocks of the Paris Basin and its margins.

(To be continued.)

NOTES ON THE PHYSIOGRAPHY OF ARRAN.

By ALEXANDER SCOTT, M.A., D.Sc.

FROM the point of view of both geological structure and physiography the island of Arran may be divided into two parts of approximately equal area. The contrast in scenery is very pronounced, the northern portion consisting of a number of rugged peaks and ridges, rising to almost 3000 feet and interspersed with deep valleys; while the southern portion is mainly moorland with rounded hills which seldom exceed 1500 feet in height. The geological structure of the former has been described in detail by the Geological Survey (Gunn, 1903), and although no systematic description of the latter has appeared, several papers on the sedimentary and intrusive rocks have been published in recent years (Gregory, 1915; Tyrrell, 1915).

Apart from the Glacial and Raised Beach deposits, the youngest rocks in the island are the Cainozoic dykes and sills, and these are not later than Miocene. The northern half of the island consists of a great circular dome of granite surrounded on the north, west, and south by metamorphic rocks of pre-Cambrian age; while on the east it abuts transgressively on Palæozoic sediments. The mountains, all of which are found in the granite area, are divided into two groups by the long north and south depression which runs up Glen Easan Biorach from Loch Ranza and down Glen Iorsa, culminating at Loch Iorsa. The eastern group comprises a number of ridges radiating from Cir Mhor, one running north-north-west over Caisteal Abhail to Creag Dubh, one south-south-east to Goatfell, and one south-south-west over A' Chir and Beinn Tarsuinn to Beinn Nuis. Subsidiary ridges branch off from each of these, as, for example, the Suidhe Fheargus ridge from The Castles, Cioch na hOighe, and Am Binnein from Goatfell, and Beinn a Chliabhain from A' Chir.

The eastern group includes a curvilinear ridge which proceeds in a general northerly direction from Beinn Bharrain over Beinn Breac (2333 ft.)1 to Meall nan Damh, and another from Beinn Tarsuinn (1819 ft.)1 to Meall Mhor. The area of high land is bounded on the north by the Chalmadale-Sannox depression between which and the coast is a range of low hills. On the southern edge is a broad plateau, about 1000 feet above sea level, and terminating in the through valley which carries the "String Road."

The hills of the southern portion only attain a maximum height of under 1700 feet, and may also be divided into two groups. Situated immediately to the south of the String Road is a large Cainozoic volcanic vent, the igneous and pyroclastic material of which gives rise to the Ard Bheinn group of hills, while to the south-east, and separated from the latter by another depression, is the Tighvein group. This is formed by a large series of Cainozoic sills which have been intruded into the Triassic sediments.

The contrast between the two types of scenery may be paralleled, to some extent, by a similar contrast which is found in Skye, where the mountainous region of the Cuillins is sculptured out of a great gabbro laccolite, while the monotonous plateaux to the north-west are made up of the Cainozoic sills and dykes. The two districts present several other analogies, which will be discussed later.

In endeavouring to determine the history of the topography of Arran, it is necessary to take into consideration, firstly, the effect of the dissection of the ancient Highland peneplain, and of the denudation which occurred prior to the separation of Arran from the mainland ; and, secondly, the effect of the denudation which has taken place since the separation of the island. It is generally recognised that the Scottish Highlands have been carved out of a plateau, which may have originally been a peneplain, and the present average height of which is between 2000 and 3000 feet. This tableland sloped gently from north-west to south-east, and many of the higher peaks of the Highlands stood out as monadnocks in the undulating plateau. It probably extended much farther to the north-west than the present land surface, and many of the north-west south-east through valleys of the Highlands were initiated by the consequent streams which drained this plateau. Superimposed on this drainage system is a series of subsequent valleys with a general north-east and south-west trend, following the direction of the strike of the Dalradian rocks, and parallel to a series of faults. In the south-west Highlands the trend is rather south-south

west.

According to Peach and Horne (1910), the second base-level of erosion occurs approximately at the 1000-feet level, but these writers