and have, as appeared to me at first, a much less flattened form, presenting in section a full round outline on that side which forms the outer edge of the tooth's curvature. A comparison of specimens. of Megalosaurus teeth with this Norfolk fragment, leaves no doubt as to their complete distinctness. On the other hand, the fragment agrees in detail, as well as in general appearance, with the right upper canine of Machairodus. The tapering of the tooth corresponds closely with that of a large-sized Machairodus canine, as shewn in the figure, one side of the tooth being a little more convex than the other. The serrated edges do not run vertically, so that the plane passing through them would divide the tooth into two unequal parts (see section Fig. 3); but, as is observable in Machairodus, the opposite serrated edges are not parallel to one another, but are curved-one slightly inwards, the other outwards. enamel on both surfaces is longitudinally split and cracked, exactly in the same manner as it is on MacEnery's specimen from Kent's Hole. Therefore, small though this fragment is, it carries, sufficiently clearly marked on it, the evidence of the ownership of Machairodus. The The specimen is too incomplete to make any discussion of specific characters useful. As to its geological age, there is every probability that it came out of the Forest-bed, whether contemporaneous, in the period represented by that accumulation, with the recognized Forest-bed Fauna, or not. The specimen is of a black colour externally, of a deep brown on the fractured surfaces, and was picked up on the shore between high- and low-water, amongst the débris of the Forest-bed. Whilst having the good fortune to add this interesting carnivor to the list of Forest-bed mammalia, I cannot let the opportunity pass of mentioning-what, indeed, has been recognized by those working at this deposit at home, but not by all writers-that Mastodon has not been found in the Forest-bed; and, that even were fragments of that genus to occur, we might have to regard them as derived from accumulations of an earlier period, just as it is possible, though not probable, that this fragmentary Machairodus canine may have been derived. EXPLANATION OF PLATE XVI. Fig. 1. Side-view of right upper canine of Machairodus. [The shaded parts of Figs. 1 and 2 represent the Cromer Forest-bed specimen; the outlined entire canine is copied from the cast of a French specimen of Machairodus cultridens, Cuv., with the curvature of which the Norfolk fragment closely agrees. The outline of M. latidens, Owen, from Kent's Hole, tapers more rapidly than the Norfolk specimen, indicating a much shorter canine.--EDIT.] Fig. 2. Front-view of right upper canine of Machairodus, showing the curvature of the serrated edge of the tooth. Fig. 3. End-view of Mr. Jarvis's specimen, showing the serrated edges which divide the tooth into two unequal parts (f anterior, i posterior edge of tooth). Fig. 4. A portion of the serrated margin of the tooth enlarged. c. c. The part above this line is enclosed in the jaw, the other letters show the corresponding parts in Figs. 1 and 2. IV. ON THE DENUDATION OF WESTERN BRITTANY. By G. A. LEBOUR, F.R.G.S., of the Geological Survey of England and Wales. roughly, the geology of the Department 1. Geology.-STATED tou may be said to consist of two masses of of granite, one to the north and one to the south, enclosing between them nearly the whole of the sedimentary rocks of the district. These consist of Cambrian slates and gneiss, Lower, Middle, and Upper Silurian slates and grits, and very small and unimportant patches of Upper Carboniferous shales. The entire mass of these deposits has an east and west direction, and occupies the central part of the Department. All the country to the north of Brest, and extending from Normandy to the Isle of Ouessant, forms part of the northern granitic mass. Between this and the tongue of land to the south of Douarnenez, including the very indented peninsula of Crozon, we have the Cambrian and Silurian rocks powerfully undulating and forming the two loftiest chains of hills in the district-the Montagnes d'Arrhée and the Montagnes Noires-which run across the country close to and parallel to each other in an east and west direction. Immediately to the south of this wide band of Paleozoic formations, comes the southern mass of granite. Like the first, this has scattered here and there, over its whole extent, numerous isolated enclosed masses of metamorphic schists, which have, by Dufrénoy and others, been referred to the Cambrian age. The coal shales mentioned above, as occurring in this district, are to be found in thin elongated patches at Quimper and at Cléden, on the west coast; their extent is utterly insignificant. About two miles south of Quimper, near the hamlet of Toulven, is to be seen a small series of horizontal beds of Tertiary age (the only instance of the occurrence of such deposits in the Department) of which more will be said presently. -- 2. Coastline. The coastline of Western Brittany is very irregular. The two great bounding masses of granite forming comparatively even and sweeping lines, interrupted only by the long, narrow, and winding creeks which are to be found at the mouths of all the rivers. These creeks are, however, quite minor features on these coasts, and are many of them hewn out of the micaceous schists which are interspersed among the granites. Where an estuary occurs in the granite itself, it is usually wider, and is bounded by flat sandy shores. The cliffs along these coasts are low, with rounded and wellweathered tops. They are higher when composed of the metamorphic schists, which are much more compact and harder to disintegrate than the granites of these parts, and naturally form bolder and more striking cliffs. The Cambrian and Silurian beds, on the other hand, which are enclosed between the two above-mentioned bands of granite, are, as a rule, characterized by high, steep cliffs, the faces of which are frequently much eroded into caverns, oftentimes of very considerable magnitude. The general line of this part of the coast is very in dented, and forms an endless number of small bays, promontories, and headlands; as may be seen by glancing at the Rade de Brest in any map. Along the southern granitic coast, the sea is very shallow for some miles, and the numerous small islands with which it is studded have exactly the same geological features as the mainland; thus showing that the southern granitic plateau has a much greater extension than the boundary of the coast alone would indicate. The Iles de Glénan are a case in point. 3. General Surface Characteristics.-The two great watersheds of the country are formed by the two central chains of hills, the space between them or "swire," which is very narrow and not much below the average height of the two flanking ranges, being for the most part covered with wet bog-land. The Montagnes d'Arrhée supply the streams running to the north and north-west, and the Montagnes Noires those flowing to the south. Descending from these hills on either side, and proceeding to the south or north, we find ourselves all the way to the sea in what appears at first sight to be an exceedingly hilly and disturbed country. The streams are innumerable, and flow at the bottom of deep narrow rocky ravines, which intersect the country in every direction. Their course is most tortuous, and continues, with scarcely any noticeable difference of width or depth, alike through the hard Silurian grits and their enclosed traps, the vertical or contorted leafy metamorphic schists, and the variously-grained, easily decomposed granites. What slight change there may be, however, is most discernible among the latter rocks, where the valleys are sometimes somewhat wider and less winding than in the former. The jagged appearance, moreover, of the rocky sides of these valleys tends to increase the mountainous and rugged aspect of the scenery. This, however, is only the result of a superficial view of the physical features of this district, and is by no means in accordance with the true facts of the case. These errors are perpetuated by the use of sections across the country drawn on exceedingly exaggerated vertical scales; quite a universal practice abroad. By drawing horizontal sections on a true scale, cutting the whole breadth of the peninsula, the height and distances being taken from the large government maps of these parts, and by carefully going over the ground along each line of section, added to a long acquaintance with the country generally, I have been enabled to arrive at the conclusions, the statement of which is the object of the present paper. Following on paper one of these lines of section (a north and south one) from the base of the Montagnes Noires to the southern sea-shore we are immediately struck by the absence of marked I have ventured to use the old north country word "swire" to express the slack between two hills. I think it might be a useful one to adopt in the description of physical features. The result would be exactly similar were we to follow the northern half of the section from the hills to the north coast. |