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154 Saunders—Geology of South Bedfordshire. pieces, or plates, are not differentiated—the shield in both is of a single piece; but it is obvious that in Cephalaspis the rostral, orbital, and cornual element predominate, whilst in Scaphaspis the discal region chiefly is represented. EXPLANATION OF FIGURES. Fig. 4. Relievo ) of Bidymaspis Grindrodi, sp., nov., from the Lower Old Bed, 5. Intaglio) Ledbury. 6. Outline of the shield of Didymaspis. 7. Bone-lacunae from the posterior portion of the shield of the same. 8. Outline of Auchenaspis. V.—NOTES ON THB GEOLOGY OF SOUTH BEDFOBDSHTBE. By J. SAUNDERB, Esq. Geology of South Bedfordshire is now being exhibited X more fully than hitherto, as the extension of the Midland Eailway from Bedford to London is opening up a series of sections in the newer Secondary rocks which characterise this part of the county. The following notes were chiefly taken during a walk made last summer along the line, between the towns of Bedford and St. Alban's (Herts). For the first few miles the excavations are slight, and exhibit only the Drift sands and gravels of the rich valley of the Ouse, though these are well worthy of careful examina- tion for flint implements and mammalian remains, which have been discovered on the north side of the river, at Biddenham, by J. Wyatt, Esq. About three miles from Bedford is an excavation in the Oxford clay ; the upper portion is dark brown merging into dark blue beneath, and it abounds in fossil wood in various stages of carboniza- tion, the colour of which ranges from brown to jet black; it is so abun- « / 9 DIAGRAM TO ILLUSTRATE THE GEOLOGY OF SOUTH BEDFORDSHIRE. a. Oxford clay. *. Greeosand. c. Gault. d. Totternhoe stone, e. Supposed bed of clay under the Lower Chalk. /. Lower Chalk, g. Chalk with flints. The dip of the strata is a little greater than that of the surface of the country. dant in places that some of the excavators fancied they were coming upon a coal-mine. Sunning through the mass of clay is a profuse abundance of roots and fibres in inextricable confusion. Belemnites are common in this bed, as is also Ammonites Calloviensis in the clearages, but the fossils are so hopelessly compressed and fragile as to defy all attempts at extrication, save in the smallest specimens. This formation extends to Ampthill, where it is more largely developed, and where 4 tunnel is carried through it immediately beneath the Park. The approaches to the tunnel exhibit a series of beds of clay, brown at top and merging into dark blue below, with intermediate bands of Saunders—Geology of South Bedfordshire. 155 hard grey limestone, ranging from a foot to eighteen inches in thick- ness. The northern approach shows an anticlinal in these lime- Btone bands. The upper beds of brown clay contain very many small crystals of selenite, which sometimes constitute one-third of the entire mass. In the lower beds the crystals are rare, but much more regular in form and beautiful in appearance, and also much larger, one specimen measuring about six inches in its major diameter. The fossils observed were bones of Plesiosaurus, one vertebra of which weighed ten pounds, spines of several species of Echini, Ostrea carinata and various other species, Pentacrinites, Belemnites, Grypheee, and Ammonites Galloviensis. Near the village of Flitwick are two cuttings in the Lower Green- sand, consisting of white and yellow sands, alternating with bands of ironstone. These beds extend beyond Sandy, in a north-easterly direction, and to Leighton south-westwards. At Silsoe, five miles east from Mitwick, are beds of a brown compact sandstone, which furnish good building material; these are also of Lower Greensand age. A short distance south from Westoning, the coprolitic bed of the Lower Greensand is exposed,1 over which is a bed of dark heavy clay (Gault?),' which in its turn is capped by a bed of drift sand and gravel. This coprolitic bed is worked in several places in the immediate vicinity for its phosphatic nodules, and furnishes the usual fossils characteristic of this stratum. At Harlington is a cutting in the drift, but not sufficiently deep to disclose the subjacent forma- tion. Between Harlington and Chalton is a cutting in the Totternhoe stone, a local representative of the chalk marl.* This occurs in a hill, isolated from the general range of hills that form the north-west escarpment of the Chalk formation. At Chalton is an extensive excavation, upwards of a mile in length, through the range of bills that constitute the watershed of the district. The combes, that have been eroded by the action of the springs that rise at the base of these hills, have many of them great local celebrity on account of. their pictnresque scenery, and the lovely landscapes that may be seen from the summits of the surrounding hills. The Totternhoe stone is exposed at the north-west end of the cutting at Chalton, where it is hard, compact, rather sandy, and of a light brown colour. The deepest part of the excavation, where it is about seventy feet deep, exposes the Lower Chalk, which is lighter in colour and less compact than the chalk marl, bqneath which is a bed of dark clay, containing many pyrites. It is somewhat doubtful whether this bed should be classed with the Gault or Chalk-marl, it has a very strong 1 See Eev. P. B. Brodie's paper " On the Phosphatic Nodules in the Lower Green- sand at Sandy, Bedfordshire."—GEOL. MAG. Vol. III., 1866, p. 163. See also Mr. J. F. Walker's paper " On a Phosphatic Deposit in the Lower Green- sand of Bedfordshire," in the Ann. and Mag. Nat. Hist. 3rd series, vol. 18, November, 1866.—EDIT. J Or Boulder-clay?—EDIT. 1 Totternhoe stone is not a local representative of the chalk-marl. * It is the top bed of chalk-marl through Bucks, and Berkshire; there is eighty feet of chalk-marl below it. See Mr. Whitaker's paper thereon, Quart. Journ. Geol. Soc, vol. xxi. p. 398 (1866).—EDIT. 156 Saundgrs—Geology of South Bedfordshire. resemblance to the Gault, but is most probably a member of the marl.1 So far as observed there appears but little difference in the fossil remains of these strata, the chief distinction being the much greater abundance of Ammonites varians in the Lower Chalk than in the other beds.* One peculiarity respecting the Cephalopods is the total destruction of tiie shell itself, its place being occupied by a brown ochreous substanee, and in most instances, when a specimen is frac- tured, the internal divisions of the chambers are most beautifully indicated by the same substance. Only one specimen has been dis- covered witih any trace of the shell; this was in the fragment of the outer whorl of a large individual, which, when entire, must have measured sixteen inches in diameter, in this case the outer shell was absent, but the internal separations were preserved. The Ammonites various varies in size from an inch to upwards of a foot in diameter, and the same remark will apply to a species of Nautilus occurring in the same locality. The shells of Ostrea, Terebratula, Pecten, etc., have not suffered the decay incident to the Ammonites and their congeners. Most of the Cephalopods are very much compressed and contorted, more particularly the Ammonites varians, which some- times present such anomalous forms as to render it scarcely recognisable. The fossils obtained from this cutting are mentioned in the subjoined list. At Leagrave is an excavation in the Drift formation, that exhibits a series of alternating sands, gravels with sub-angular flints, and clays, containing rolled fragments of fossils from the Secondary strata. At the south-eastern termination of the cutting a member of the Lower Chalk appears, that has been coloured a light yellow by the percolation of water through the superincumbent bed of clay. About midway between Leagrave and Luton is another bed of the Lower Chalk. This is hard and compact, with almost a metallic ring when struck with the hammer, and so indurated, that blasting has been necessary in working it. The natural cleavages have a greenish tinge. This bed has, numerically, a great many fossils, but the species are few, the most prevalent forms being Terebratula and Inocerami. At Luton the Lower Chalk is softer than the pre- ceding, and runs along the valley of the Lea as far south as Wheat- hamstead. Between Luton and New Mill End is a series of cuttings in the Upper White Chalk. This contains an abundance of flints, in layers at irregular intervals, and also several thin seams of a grey clay, somewhat resembling fuller's earth. These clay bands may be seen at Harpenden, where the roads have been altered for the con- venience of tiie new railway. The fossils from these cuttings are those characteristic of the Chalk-with-flints, of which a list is subjoined. From Harpenden to St. Alban's the Upper Chalk is exposed, capped with drift sands and gravels, and as we approach the latter town 1 When the Lower Chalk is full of water it presents the appearance described here by the author, of a "bed of dark clay;" the Lower Chalk is always rich in iron pyrites.—EDIT. 2 A. variant is remarkably abundant in the Totternhoe stone of this part.—EDIT. Saunders—Geology of South Bedfordshire. 157 these accumulations are seen to increase in depth, and contain an abundance of large flints only slightly rolled, as well as dark pebbles obtained from the disintegration of older conglomerates.

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