H. M. Jenkins—Surface-Geology of . 199 these points have received confirmation, as time flowed on, from nearly all the most trustworthy of his contemporaries. So lately as February, 1867, the President, Mr. Warington W. Smyth, in the name of the Geological Society, conferred upon Mr. Poulett Scrope the highest honour at the disposal of that body, namely, the Wollaston Gold Medal, in recognition of his researches into the nature and origin of volcanos; with which line of investi- gation his name will always be indissolubly connected.

II.—ON THE SUBFACE-GEOLOGY, DENUDATION, AND "FOBM OP THE GBOUND " OP BELGIUM. By H. M. JENKINS, F.G.S., Secretary of the Royal Agricultural Society. p review of my " Eeport on the Agriculture of Belgium," which X appeared in the last number of the GEOLOGICAL MAGAZINE, illustrated by a reprint of the map which originally accompanied it in the " Journal of the Eoyal Agricultural Society " (2nd series, vol. vi., part 1), has induced me to offer some further remarks on the surface-geology of that kingdom while the subject is still fresh in the recollection of the readers of this Magazine. A mere glance at the map is sufficient to impress the geologist with the remarkable parallelism existing between the boundary lines of the surface-deposits and certain contour-lines, which show what the late Professor Jukes delighted to call the " form of the ground." The accompanying section, drawn from Ostend, on the north-west, past Ghent, and through Nivelles, KTamur, and Dinant, to near Longwy, in the south-east, will illustrate my meaning. Ostend is situated on the seaboard margin of a Polder-plain, the alluvial deposits which constitute its environs having been reclaimed from the sea chiefly within the historic period. Proceeding in a south- easterly direction, the Polder alluvium is succeeded by a broad belt of sand (the sands), which, although it appears almost a' plain to a casual observer, has in reality a slight inclination, so that at about two-thirds of the distance across it we reach a height of 75 feet above the sea-level; but, except in the Campine, at the extreme east of Belgium, this sandy zone never attains a much greater elevation. The perfect inclination of this zone is interrupted, and its gradual rise is masked, by the valleys of several tributaries of the (Escaut), as well as by the wide and deep valley of that river itself. South-east of the sandy zone we enter upon a broad belt of loam, generally known as the Limon de Hesbaye, or Loess, and im- mediately the gradient of the surface-incline increases to a very remarkable extent. While previously the gradient has not been more, and has generally been less, than 75 feet in 20 miles, or less than .three inches per mile, we now find the line of 150 feet elevation running at a regular distance of about three miles from that of 75 feet, across two-thirds of the kingdom of Belgium. We have here, therefore, the following noteworthy phenomena:—(1.) A gradient 200 H. M. Jenkins—Surface-Geology of Belgium. of from 20 to 25 feet per mile, instead of one of 3 inches ; (2.) The parallelism of the lines of 75 and 150 feet elevation; and (3.) The parallelism of these lines with the line of junction of the Campine sands and the Limon de Hesbaye. South-east of the 150 foot contour-line the inclination of the surface again becomes comparatively gradual, though somewhat irregular and more interrupted than was the case in the sandy zone; but from the 150 foot line to the valley of the , a distance of about 60 miles, the rise is not more than about 350 feet, the north bank of the river having an average height of about 500 feet above the sea level. This rise indicates a gradient of less than six feet per mile, or not much more than one-fourth of that just noticed—a fact sufficiently remarkable when placed in contrast with the former abrupt declivity, and with •what is seen- on the south bank of the river valley. The line of 600 feet elevation runs about two or three miles to the south of the Meuse valley, and is succeeded southwards, at a mean distance of about four miles, by the line of 800 feet elevation, the gradient between these two lines being, therefore, as high as 50 feet per mile. The succeeding flatness, as already described in the previous cases, is once more seen south of the 800 feet line, for it requires a journey of about 20 miles (except in the extreme east of the ) to reach the line of 1,000 feet elevation, thus showing that the gradient has fallen to about 10 feet per mile. South of this "inclined plane" we meet with another and still more abrupt gradient, and then reach the broken plain and the isolated eminences of the Higher Ardennes. The significance of these facts to the geologist and the physical geographer appears to me so obvious that I shall mention but very briefly the conclusions which they forced upon my mind. In the first place, the Limon de Hesbaye rarely crosses the gorge which forms the Meuse valley. I have, therefore, for agricultural purposes, mapped all the tract of country south of the Meuse as "Strong Plateau-land;" but geologists know very well that the and the Ardennes, which comprise that tract, consist of certain Paleozoic rocks, overlain in places by patches of drift (Caittoux Ardennais) near the numerous watercourses. This drift, containing rocks of Ardennes origin, is also found beneath the loam in the Hesbaye and beneath the sand in the Campine. North of the Meuse, and at a lower level, therefore, is the more or less broken plateau, having the Limon de Hesbaye as its surface- deposit ; and north of this loam, at a still lower level, is the plateau composed of the Campine Sands. This terrace arrangement, in reference to the geological age of the surface-deposits of Belgium, seems to me capable of but one interpretation—namely, that the Ardennes drift ( Cailloux Ardennais) is the oldest of the deposits, the Limon de Hesbaye the next in succession, and the Campine Sands the youngest of all, with the exception of the Polders, which we know to have a historic date. The Campine Sands were regarded as contemporaneous with the Limon de Hesbaye by M. Dumont, and as older than it by M. Palaeozoic Bocks. 4. S (150 MILES). e (Loess). N COAST TO THE HIQBEB ARDENNE a a' a" Planes of Marine Denudation. Near Audenarde Campine Sands 3. Limon de Hesbay 2. SECTION FROM THE BELGIA Valley of the Scheldt. Polders. 1. Near Ostend. N.W. 202 H. M. Jenkins—Surface Geobgy of Belgium. d'Omalius d'Halloy; but I venture to think that the physical rela- tions of the deposits prove the higher antiquity of the Limon de Hesbaye. The importance of the question, however, should lead to further investigations than my agricultural engagements left me time to prosecute. Mr. Godwin-Austen, in his paper "On the Kainozoic formations of Belgium," remarks1:—" The age of the Campine sands has been very often discussed. They are now very generally referred by Belgian geologists to the Syst&me Diluvien. Though the true Campine sand has never been found to contain animal remains of any kind, it overlies a surface with Elephas primi- genius. It is certainly older than the Polder mud deposits and their equivalents, the peat growths. However, there may still be a great range between these extreme periods. In like manner, the Loess (Limon de Hesbaye) overlies the gravel beds in which the fragmentary remains of the great Pachyderm fauna occur. Both the Campino sands and the Loess are subsequent accumulations to the Ardennes quartz pebbles; but the occurrence of these pebbles at the base of both does not necessarily connect them with either, but it suggests that these two accumulations must be nearly of the same age, and such, it seems, was M. Dumont's latest view." The occasional occurrence of freshwater and land shells (Succinea, Pupa, &c.) in the Limon de Hesbaye has led to the opinion that the whole mass is of freshwater origin. I find it difficult to subscribe to this view, and still more so to that which ascribes a contempo- raneous formation to the Loess and the Campine sands; as in that case the sand must have been deposited in the deeper water! With reference to the causes which have produced the present " form of the ground" in Belgium, these terraces seem to me to demonstrate the truth of Professor Eamsay's idea of "planes of marine denudation,"% so far, at least, as that country is concerned; and in the accompanying section I have shown by a dotted line where I conceive the planes of marine denudation left the surface of the country to have its present physiognomy chiselled out by the force of subaerial agents.3 The delineation of the contour lines on a map of the surface- geology appears a most important adjunct. In the map of Bel- gium, it is instructive to observe the remarkable coincidence in the " behaviour " of the contour lines and in that of the geological boundaries, and especially how they similarly become squeezed together in the east and widen out in the west. The whole country

1 Quart. Journal Geol. Soc, vol. xxii., p. 250. 2 A somewhat similar view of another region has been proposed by Mr. G. A. Lebour to explain the surface-features of western Brittany. (See GEOL. MAG. Vol. VI. 1869, p. 442.)—EDIT. 8 May we not regard the far greater diversity {i.e. the more denuded character) of the surface covered by the Limon de Hesbaye than of the Campine sand region as an additional piece of evidence in favour of the previous denudation of the former region. The eminences in the loamy region are numerous, and not unfrequently rise to a height of from 300 to 400 feet above the neighbouring valleys, while in the Campine sand district a difference of level of 50 feet cannot be seen except in the extreme east—the true Campine. G. Maw—Rhcetic Beds in Shropshire and Cheshire. 203 is higher and less diversified in the east than in the centre of the Kingdom; but in the extreme west it begins to rise again, so that if a certain portion 'of France had been included, the map -would probably have shown the existence of a great surface-trough with a nearly north and south direction.

UL—ON THE OOCUBBENCE OF THE BOXTIO BEDS IN NOBTH SHBOP-

SHIEB AND ClIESHIBB. m

By GEO. MAW, F.G.S., F.L;S., etc. fTlHE outlying mass of Lias on the borders of Shropshire and _|_ Cheshire is so thickly covered with Boulder-drift, that its line of boundary throughout almost its entire circumference is very obscure. The direct sequence from the underlying Keuper Marls is FIG. 1. scarcely anywhere visible, and I be- lieve no record of the occurrence of the Avicula contorta zone has hitherto been published. About three years ago I noticed near Audlem an exposure of fissile shale, closely resembling the " Paper- shales " of the Garden-cliff and other Gloucestershire sections, and more recently procured a small series of fossils confirming their identity with the Eheetic beds. The strata represented in the ac- companying section, Fig. 1, occur in a lane-cutting, near Audlem Mill, immediately to the south of Audlem Eailway Station. They dip about 7° to the east, and include the following beds:—A, drift of variable thickness; B, about 8 feet of black fissile shales (Paper-shales); o, hard band of rock, about 6 inches thick; D, a repetition Section near Audlem Mill. of black flaky shales, about 15 feet * Junction not visible. thick, passing downwards into a light buff marl, E, 6 feet thick; but the junction is obscured by the Eailway Bridge. The buff marl graduates into soft red Keuper marls, F, about 5 feet thick, succeeded by hard variegated marl, G, exposed in the bed of the brook. The black shales, D, abound with Avicula-contorta, and Mr. Etheridge, who has kindly examined the fossils for me, has also determined, in the shales, D, Pvllastra arenicola and Cardiwn Bhati- cum; and in the bed B, an Axinus and Pidlastra arenicola. I could find no continuous sections showing the junction of these