through this part of Wiltshire in their natural order of succession; as is shown in the following section (Lign. 118), in which the subdivisions of the Chalk and Oolite, from the Upper or flinty Chalk down to the Oxford Clay, are seen in a nearly horizontal and conformable position. LIGN. 118.-DIAGRAM-SECTION THROUGH THE WILTSHIRE CHALK-DOWNS TO THE OXFORD CLAY. 1. Upper and Lower White Chalk. 2. Upper Greensand. 3. Gault. 4. Lower Greensand 5. Portland Oolite. 6. Kimmeridge Clay. 7. Coral-rag. 8. Oxford Clay. A bed of 14. KELLOWAYS ROCK AND CORNBRASH. gritty and sandy limestone, a few feet in thickness, and sometimes ferruginous, is intercalated with the lower portion of the Oxford Clay in the South of England and in Yorkshire, and is remarkable for the abundance of molluscan remains which it contains. It is called the Kelloways rock; hence a common species of ammonite in this deposit is named A. Calloviensis. Cornbrash.-Under the Oxford Clay a hard rubbly limestone, from ten to twelve feet thick, sometimes passing into clay and sandstone, is generally met with, which, like the Kelloways rock, swarms with many species and genera of marine shells, associated with other fossils. This bed is provincially termed Cornbrash. Subjoined are figures of a few Cornbrash shells from the neighbourhood of Scarborough in Yorkshire, which were first described by Mr. Bean.* *See Mag. Nat. Hist. 1839, vol. iii. p. 57. In the South-west of England, the Cornbrash, which is persistent as a peculiar shelly deposit from the South to the North of England, is succeeded downwards by, 1st, the 2. Bulla undulata. (Occurs also in the Great Oolite of Minchinhampton.) 4. Anomia semistriata. 5. Cardium globosum. 6. Isocardia triangularis. Hinton Sands and Forest Marble, together about 100 feet in thickness; 2nd, by the Bradford Clay, about 50 feet thick; 3rd, the Great or Bath Oolite, varying from 40 to 120 feet in thickness; 4th, the Fuller's Earth, a series of marly and calcareous beds, of very variable thickness, sometimes 130 feet thick; and lastly by the Inferior Oolite, a group of calcareous and sandy beds, often ferruginous, and sometimes upwards of 200 feet thick. The Inferior Oolite extends into the Midland counties and Yorkshire, although very reduced in thickness; but the other members of the Lower Oolite beneath the Cornbrash are variously represented in the Midland and North-eastern districts, and in the North British area represented by the Oolites of Skye and Brora. Instead of marine calcareous deposits being the predominant feature, sandy and clayey deposits form the mass of the beds; and land-animals, such as insects, the Megalosaurus, and a few mammals, are found in them, whilst remains of land-plants occur occasionally in great profusion. In these circumstances we have indications that the Lower Oolitic rocks of Southern England were formed in a comparatively deep sea (though not of so uniform a depth as that of the preceding Middle and Upper Oolite periods), and that the coast-line of the then existing land lay probably at no great distance to the north-west of our Midland Oolitic area.* The Forest Marble and Bradford Clay.-The fissile sandy oolitic beds, or tilestones, of the Forest Marble, have afforded remarkably fine specimens of ripple-markings and tracks of shell-fish and crustaceans; and have evidently originated as local shallow-water deposits, full of broken shells. The more compact shell-beds form the blue limestones, or forest marble of Wiltshire. A series of clay-beds and thin limestones succeed, but are sometimes merged into the Forest * The student is referred to Mr. Morris's lucid comparison of the Oolitic rocks of Gloucestershire, Lincolnshire, and Yorkshire, in the Quart. Geol. Journ. vol. ix. p. 317, for detailed descriptions and much valuable information on this subject. The admirable memoir by Mr. Lonsdale on the Geology of the country around Bath should be consulted by those desirous of more ample information on the Oolite of that part of England; Geol. Trans. 2nd ser. vol. iii. p. 242,-and Professor Phillips's Geology of Yorkshire, for a full account of the Oolite system of the eastern moorlands of that County. Marble above, or the Fuller's Earth beds below. These clays are remarkable in the neighbourhood of Bradford, in Wilts, for the remains of a particular species of crinoid, called the Pear-encrinite of Bradford * (Apiocrinus: Medals, p. 288), which in some places occur under circumstances apparently indicating that the animals still occupy the spots where they grew. The clay is spread over the surface of a stratum of limestone, and many of the stems of these Stone-lilies are upright, with their root-like bases attached to the calcareous rock; and numerous articulations, once composing the stems, arms, and body of the animals, are scattered at random through the clay.† 15. THE COTTESWOLD HILLS.-As the elevated tract of country called the Cotteswold Hills, which extends for thirty miles through the county of Gloucester, in a N.E. and S.W. direction, having an average breadth of ten or twelve miles, exhibits the principal characters of the jurassic series of the South-west of England, the following brief description of this interesting and typical tract will be highly useful to the student.‡ The surface of this district has a general inclination to the S.E., its eastern borders having an elevation of about 400 to 500 feet above the sea; whilst the western ranges from 600 to 800 feet, and the culminating point, Cleeve Cloud, is 1134 feet high. The branch of the Great Western Railway from Swindon to Glouces *Pictorial Atlas, pl. 1. + Manual of Geology, 5th Edit. p. 307. This account of the physical geography and structure of the Cotteswolds was communicated to the author by Professor Woodward, formerly of the Agricultural College, Cirencester, now of the British Museum. The student should also avail himself of Mr. Hull's paper on the Cotteswolds, in the Geol. Soc. Journ. vol. xi. p. 477; and his " Memoir on the Geology of the country around Cheltenham," in the Memoirs of the Geological Survey, 1857, illustrative of the Sheet 44 of the Geological Survey Map. ter passes through the centre of the district, and affords a key to its geological structure. These hills are entirely composed of two series of oolitic limestones, separated by a bed of clay known to geologists as the " Fuller's Earth." The strata are inclined to the S.E., at the rate of about 1 in 130, or less than half a degree; yet this inclination is greater than that of the general surface, and sufficient to carry the hill-strata beneath the newer formations on the S.E.,; whilst on the north-western boundary they terminate in steep escarpments, that are broken and indented by numerous deep and picturesque valleys. In order to obtain a general idea of the nature and succession of the strata of the whole district, we may conveniently pursue the well-known Roman road termed the "Irmin Way," which, coming from Newbury through the Wanborough downs, runs almost in a straight line to Cricklade, Cirencester, Birdlip, and Gloucester, and traverses in succession the whole of the oolitic strata, in the following order : 1. Portland stone. 2. Kimmeridge clay. 3. Coral-rag. 4. Oxford clay and Kelloways rock. 5. Great Oolite: subdivided into Cornbrash, Forest marble, Bradford clay, Bath freestone, Stonesfield slate. 6. Fuller's earth. 7. Inferior Oolite. 8. Lias. 1. The Portland stone is extensively quarried near Swindon Old Town: 2. The Kimmeridge clay forms the valley in which the Swindon station and the New Town are situated: 3. The Coral-rag rises up from beneath the clay, and constitutes the hills about Stratton, Saint Margaret's, Pen Hill, and Blunsdon: 4. The Oxford clay occupies the whole of Braydon Forest, and the wide valley around Cricklade, but is covered in many places by thick beds of oolitic gravel. 5. At Driffield Cross-ways the Cornbrash is seen in the small quarries from which the road-stone is procured; and in descending the hill towards Cirencester we pass to the Forest marble, a thin-bedded stone, well shown in the quarries at Preston, from which much of the roofingstone and planking, so extensively used in the neighbourhood, is obtained. A bed of clay is usually found separating the Forest marble from the Bath freestone, and is therefore the equivalent of the Bradford clay Beyond Stratton the road lies over the Bath freestone (or " Hampton stone") as far as Highgate, where several deep valleys expose the Stonesfield slate, Fuller's earth, and Inferior Oolite. The quarries near Birdlip also exhibit the Inferior Oolite, and the remainder of the road to Gloucester rests upon the Lias. If an Artesian well were sunk at Swindon New Town, it would probably pass through the above-mentioned strata, from the Kimmeridge |