Excursion to Guildford and Chilworth. June 1st, 1872 - Geologists' Association excursion

From: A record of excursions made between 1860 and 1890. Edited by Thomas Vincent Holmes , F.G.S. and C. Davies Sherborn, F.G.S. London: Edward Stanford [For the Geologists’ Association], 1891. Source: Cornell University copy on the Internet Archive (Public domain work)

Directors: Prof. T. Rupert Jones, F.R.S., and C. J. A. Meyer, F.G.S. (Report By Prof. Jones.) (Proc. Vol. iii. p. 93.)

Note: [Guildford was first visited by the Association in 1869, during the cessation of issue of Proceedings. From a brief record of the event in the Geol. Mag. for 1869, p. 331, we learn that the chief object in view was "the examination of the several kinds of strata forming the hills and vales in the vicinity of Guildford, Mallard, and Chilworth." The leaders were the President (Prof. Morris), C. J. A. Meyer, and Prof. T. Rupert Jones. The report of the second excursion is given below.]

The members met Prof. Rupert Jones at the Guildford Railway Station, and proceeded to examine the section of the Woolwich and Reading Beds just north of the station. This section was described by Prestwich in 1850 (see Quart. Jour. Geol. Soc., vol. vi., p. 260, fig 6), not long after it had been exposed by the railway-cutting. A year ago it was laid bare afresh when the railroad was widened, but already the slipping of the clays has obliterated some points of interest. Traces of the shell-beds, with Cyrena and Ostrea, from the basement bed of the London Clay, are to be found at the base of the telegraph-post, Ioo yards south of the road-bridge, and the underlying mottled clays, with a dip of 4° to the north, are easily recognized for about 190 yards to the south, where a small valley (about fifty yards across) has been formed by denudation out of the sands and lowest green sandy clays resting on the Chalk, which forms the northern foot of the Hog's Back or Surrey range. Here the Chalk is seen to be traversed in every direction with fissures, often slickensided; some empty, some filled with vein-flint, and some with loamy stuff. Nodules, and occasional thin lamina of flint, follow the dip of about 6= to the north, and are often in a crushed condition. Bands of manly Chalk also lie on the same plane. Some Echinoderms were met with.

Mr. Godwin-Austen, F.R.S., now joined the party, who next visited the much larger excavation of the Chalk at the entrance of the railway-tunnel. Here the dip, well marked by flints and manly bands, is about 12° to the north. Fossil sponges, echinoderms, Inocerami, &c., abound in this pit. The usual chalcedonic and quartzy interiors of hollow flints attracted notice, and Prof. Rupert Jones drew attention to facts that seemed to him to bear evidence of flint being a pseudomorph after Chalk. Leaving this instructive section, and following the road out of Guildford towards Godalming for nearly a mile, the party turned off to the right along a country road parallel with the Chalk range, but separated from it by the deep valley cut along the strike of the soft Gault. This led them to a quarry in the Lower Greensand on the escarpment overlooking the pathway to Losley. In this section of those Neocomian beds known as the Bargate stone, the water-worn sand of quartz, ironstone, lydite, and hard green silicates is so largely mixed with calcareous fragments (the debris of shell-beds, polyzoan reefs, &c.), that it is here and there cemented together compactly enough to serve as a building-stone and for road-metal. Mr. Meyer, working here, has made this quarry classic ground, and on this occasion he kindly pointed out the several species of Terebratula, Avicula, Polyzoa, and other fossils that are peculiar to this formation, or that link it with that at Upware and other places. Especially he directed attention to the horizon at which he obtained an unrolled tooth of Iguanodon, indicating the existence of this great Dinosaur at perhaps the latest period to which any of its remains are as yet known to belong. The false-bedding of the sands, due to the southward set of prevalent tides and currents, and the probable origin of their materials from the old Palaeozoic ridge or shoal, as taught by Godwin-Austen, who first made out its existence and history, were also studied. The formation of the escarpment was also noticed by Mr. Meyer. The geologists then retraced a portion of the route until they crossed the Portsmouth road at the foot of St. Catherine's Hill, and then went down to the ferry, where St. Catherine's Spring issues beneath the hill from a little cave in the red orange-tinted sand, draped with deep green mosses. The ferry-boat placed them in view of the picturesque cliff of rich-tinted sand, bearing St. Catherine's ruined shrine a-top, on the right hand, whilst the flat alluvial valley of the Wey, grassy and wooded, led away towards the white cliffs of quarried Chalk opposite.

The Guildford gap, for thirty feet at least, has been found by boring to be occupied by bouldered Chalk, and other detritus, due to the destructive and yet conservative agencies of nature. Threading the grassy paths of Shalford Park the tourists came to the turnpike-road, and entered a lane on the soft irony beds of the Lower Greensand, and followed their strike along the woods, with the red-yellow sands of the hill on the right, and the Gault valley on the left, for about a mile, until a short field-lane, crossing the Gault and Upper Greensand, led into the Chalk-marl quarry below Warren Farm. There, as Mr. Meyer explained, the loss of the clay-beds (Gault) from below by their having been squeezed out along the southern side, had allowed the hard marl-rock to subside inwards suddenly at the escarpment, and to rest at a high angle (70° and more), whilst the Chalk of the hill-range above dips only five or six degrees. As the hard rock-bands here quarried for lime are followed end-on along the strike," open to day, the backs of lower beds form one side of this deep, narrow pit; and the truncated edges of these somewhat bent and much fissured strata warn the instructed eye of the danger of standing either below them or above them, lest either rain or drought should detach their clinging surfaces on the sloping bed plane. The down-turned edges of the strata, under the sward of the hillside, are also observable, having been bent over and downwards by the combined action of rain, frost, and snow, on the slope of the hill. Large Ammonites and Nautili are the chief fossils met with here; but Pecten Beaveri and Terebratula are also found. In an old excavation in the lane Siphonia has been found in the representative of the Upper Greensand, which is underlaid by dark green sandy clay and Gault, turned up at a high angle (and probably squeezed out) in the breadth of a few yards, before the iron-sands are reached on returning to the hill-side.

Once more continuing the walk along the woods, and crossing the picturesque transverse slopes and gullies leading down into the fertile Gault valley on the left, the party came to the foot of St, Martha's Hill, or St. Martyr's Hill, for martyrs (Mr. Godwin-Austen said) were burnt on the hill by the pagan Saxons; and St. Martha was one of these Romano-British sufferers. Before mounting this hill of sand, seamed irregularly with ironstone, some of the party descended the Halfpenny Hatch Lane, leading down towards the East Shalford bottom, and saw a section of sands and calcareous sandstones, with fuller's earth bands and pebbly beds, similar to that in the quarry on the other (western) side of Guildford.

On the hill-top is St. Martha's Church, enshrining (it is said) the spot of martyrdom, and including some of the structure of the Roman watch-tower. The wide stretch of Tertiary beds on the north, and the broad expanse of Wealden beds on the south, were pointed out. On this elevated ground Prof. Rupert Jones spread his diagrams and maps of Jurassic and Cretaceous seas and lands; whilst Mr. Godwin-Austen told how the underground structure of south-eastern England is connected with that of the Boulonnais, Belgium, the Ardennes, and Westphalia; and how the folds and ridges of Palaeozoic rocks which, in those countries, bear up, either at the surface, or just beneath the Chalk or the attenuated Oolites, valuable coal-beds, are continued through, in a broad sweeping line, underneath parts of Surrey, Kent, and Sussex, until visible again near Frome, in the Bristol coal-area, in North Devonshire, South Wales, and the south of Ireland. The old faults and fissures affecting this linear tract of old strata had long before the Coal-period raised and depressed the lands and sea-beds; and as a great spur of the old Scandinavian lands, this tract afforded ground for the littoral growth of the jungles that formed the coal on its oscillating borders, and in its lagoons, now shut up by bars, and now losing their marsh features by influx of the sea. Succeeding ages still brought oscillations and changes, until the Jurassic seas crept over this old ridge or shoal, and the Cretaceous seas quite buried it, at first in sands and clays, and ultimately by the calcareous ooze of oceanic depths.

But again another contracting crush of the earth's crust operated, on the old weak lines, and the buried ridge slowly uprose, and its coatings of thick strata were worn off by sea and rain, making pebbles and sands for the Lower Tertiaries; and, still rising, it was at length laid bare in the Franco-Belgian and the Bristol areas, whilst our Wealden valley of elevation, and those of Kingsclere, Shalbourn, and Pewsey, show where its uneven back approaches near the soil.

After Mr. Godwin-Austen's lecture the geologists listened to Prof. Rupert Jones while he explained the beautiful and complex Weald, and pointed out the many Lower Greensand hills and knolls which fringe the northern edge of the valley, and give to this tract of country its far-famed picturesque beauty.

Prof. Jones clearly showed that the hills and vales coincide with the harder and softer strata, brought up by grand but gentle curves, in orderly arrangement, round a long elliptic dome, reaching from Alton on the west to Hastings and, beyond the Straits, to France, and worn down by natural agencies, of long continuance, from a high broad ridge to the present comparatively low series of lesser ridges.