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now inhabits the Cape of Good Hope and New Holland. In the midst of these leaf-beds, in Studland Bay, freshwater shells of the genus Unio attest the freshwater origin of the white clay. The fruit of a member of the Arelia family, now confined to North America, New Zealand, Japan, and the East, has been found at Bournemouth by Mr. Mitchell. Fine specimens of the leaves of a Palm (of the genus Sabal) have been found at Studland and Corfe. The river of that period may have passed through a district of granitic and syenitic rocks which brought down these pure kaolin clays. The coarser materials and quartzose grits were probably drifted from their original position either by periodical or intermittent floods.

The occurrence of isolated Tertiary patches resting here and there on the Chalk, of which the one at Tollard Royal is furthest from the central mass, leads to the supposition that denudation has removed the large masses which intervened, and, as has been already hinted, probably extended far over the Chalk below.

The heaths of Bere Regis, Affpuddle, and Piddletown, are here and there pitted with circular conical hollows, resembling the upper portion of an hour glass; they vary from 60 to 80 yards in circumference; the largest is 280 yards round. They are supposed to be swallow-holes, the result of the dissolution of Chalk by means of the carbonic acid contained in the rainwater, and the subsidence of the superjacent sands into the resulting vacuum causing a depression of the surface like that which takes place in the sands of an hour-glass soon after it has begun to run. The Rev. O. Fisher considers that the formation of these pits was subsequent to the outspread of the superficial gravel.

SUPERFICIAL GRAVELS, &c.-Gravels and Brick Earths cover the surface of the heath-lands, as well as large portions of the Chalk and the Oolites, on the border-lines of the Vale of Black

more.

The High-level Gravels are all rounded by water-action and originate from beds of which we have fragmentary traces in several parts of the county, but which do not now exist nearer than Cornwall, porphyry, granite, and quartz being their constituent parts; they cover the table-land between Bournemouth and Poole, which forms the eastern extremity of the extensive tract of land of which Picket Plain and Ochnell form the northern boundary, and were probably spread out previous to the wearing away of the surface of the present existing valleys. The lower gravel beds are represented largely throughout the county, not only covering the deep combes which intersect the coast line, but

a Lyell, Student's Elements of Geology, 1871, p. 238.

lie at the base and sides of many of the inland valleys. Those of the Stour and Piddle have yielded remains of Elephas primigenius and Rhinoceros tichorhinus; at Gains Cross near Durweston tusks of the former and teeth of the latter were met with in the railway-cutting in a bed of flint-gravel 60 feet above the river. Mr. Shipp (of Blandford) has a good collection of the remains of these pachyderms, from a pit in the nursery-gardens between the town of Blandford and the turnpike-gate on the Dorchester road; molar teeth of Elephas primigenius were found some years ago at Dewlish, in a tributary of the river Piddle. The Avon too has yielded elephants' teeth in gravels 40 feet above the river. Elephant, Bison, and deer-remains were exhumed from a bed of gravel at a combe at Encombe, the seat of the Earl of Eldon.

There are evidences of man's occupation in the cliffs near Bournemouth in the occurrence of flint-implements among the gravels 120 feet above the sea-level. Owing to the absence of organic remains it is impossible to decide as to the origin of these gravels, whether they result from fluviatile or marine agency. Mr. Codrington considers the gravels covering the table-lands at the highest levels are of far greater antiquity than the valley gravels of the rivers, which were probably formed previous to the disruption of the Isle of Wight from the mainland; also that the rivers reaching the sea by Poole Harbour, Christchurch, and Southampton were affluents to an estuary opening into the sea in the direction of Spithead.

The last movement appears to have been one of subsidence, and the occurence of several submerged forests around our coasts gives good reason to lead to this supposition. Those of Bournemouth and on the north side of Poole Harbour, Sir Charles Lyell makes an exception to, and attributes their submergence in modern times to the washing out of the subjacent sandy strata on which they rested, and not to a general subsidence or change of level. In several parts of the county, especially on the chalkuplands, drift-beds occur of local origin varying from flint-rubble and brick-earths to sandy clays. Spongites, Echinoderms, and Brachiopods (the usual Chalk fossils) are plentiful in these deposits, which represent the redistribution of the older gravels during the Pleistocene age.

SUBAERIAL DEPOSITS.-Chesil Bank. This remarkable beach runs from Portland to Burton Bradstock, a distance of 18 miles.

a See a paper "On the Formation of the Chesil Bank," by H. W. Bristow, and W. Whitaker; Geol. Mag. vol. vi. p. 433, (1869). Also J. Coode in Proc. Inst. Civ. Eng. vol. xii. p. 520, (1853).

Messrs. Bristow and Whitaker consider it to have been an ordinary beach subsequently separated from the mainland by denudation. It is connected with the mainland from Burton to Abbotsbury, where a narrow channel, the Fleet, which extends to Wyke Ferry, separates it. At Abbotsbury its base is about 170 yards in width, and its crest 22 feet above the level of the sea. At Portland its base is 200 yards wide, and its crest 42 feet in height. The separation of the land from the beach is, doubtless, owing to the configuration of the coast-line, which is without any high land or cliff from Burton to Abbotsbury; and the several streamlets which, through the imperviousness of the subsoil, and eastward trend of the coast, are diverted from their seaward course, succeed each other, and rill after rill by their united power attain sufficient force to excavate a channel, while the influx and reflux of the tide have contributed towards the formation of the Fleet, on whose bosom nearly 1000 swans roam,— the unique and enviable possession of the Earl of Ilchester. The Isle of Portland has acted as a base or breakwater in the formation of the Chesil Bank. Between Studland and South Haven there is a large accumulation of shingle, derived from the submerged beds as well as from the re-formation of older gravels.

The raised beach at Portland Bill consists of pebbles cemented together with comminuted shells; it is 30 or 40 feet above the sea-level, and about three feet thick. A projection southward shows another conglomerate with shells, chiefly Littorina littorea, Littorina littoralis, and Patella vulgata. This ancient beach terminates after a course of 250 yards. A bed of shingle caps the cliff at the Bill, and extends some way inland. Traces of an upheaval are absent on the mainland owing to the destructible character of the coast line. There are some other instances of subaerial deposits in the county; the most remarkable of these is at Blashenwell, between Corfe Castle and Kingston, where a tufaceous deposit about ten feet thick, containing land, fresh-water and marine shells, bones of animals, and wood, is spread over the clays of the Hastings Sands at their junction with the Purbeck Beds; it appears to have been the site of a small lake. which became silted up by the deposition of the lime which the water through which it passed held in solution. The source which supplied the water of the lake still exists, and flows into the Corfe river by the channel it has cut for itself through the tufa. The presence of marine shells may be accounted for hy the agency of man, during the establishment of an ancient settlement on the banks of the lake; this supposition is strengthened by similar evidences in the neighbourhood, two of which are close at hand on the Kimeridge Cliffs, shewing a lengthened occupation by man, and where the remains of sea molluscs, bones of animals, and the accumulated fragments or refuse of

human food, are present. It seems scarcely possible that any depression of the Corfe Valley on the north or south of the Chalk-range could have been the means of introducing a member of marine life even with the aid of a tidal river.

Until recently the Coal Measures were supposed to offer the only proofs of an ancient flora, but the presence of plants at every geological period is now incontestably established. The Devonian epoch presents Coniferæ, Sigillaria, Calamites, and Ferns, as well as fruits such as Cardiocarpon and Trigonocarpum, which are also Carboniferous. The earliest known Insects are in the Devonian strata of St. John's, New Brunswick. The Permian flora have a resemblance to that of the coal-period: the Trias plants are chiefly analogous to those of the Secondary rocks. During the Oolitic period the abundance of the Cycadea compared with the diminishing ratio of Equisitaceae and Ferns points to the existence of a clearer atmosphere and lower temperature, although a higher one than that which now prevails in Europe. Among the vegetable remains of the Lias, several species of Zamia have been found at Lyme Regis. At the base of the Upper and Lower Lias, respectively, Insect-beds occur; containing, besides Insects, small Fish and Crustacean marine shells as well as Ferns, Cycads, and leaves of monocotyledonous plants, and apparently brackish and fresh-water shells. The Insects include wood-eating and herb-devouring beetles, and some grasshoppers. There are evidences of a terrestrial and marine vegetation from the lowest to the uppermost beds of the Oolites, and, though the sequence of the genera has not as yet been traced through each successive stage, they reappear between intervals of several periods. The flora of the Wealden is characterized by a great abundance of Conifera, Cycadea, and Ferns, and by the absence of leaves and fruits of dicotyledonous angeiosperms. Gyrogonites, or sporevessels of the Chara, so plentiful in the Tertiary strata, were found in 1855 in the Hastings Beds of the Isle of Wight. The Miocene Beds of Europe which have probably their only English equivalents at Bovey Tracy in Devonshire, present a vegetation differing little from that of the present day. The plants of the submerged forests of our coasts at Cromer, Torquay, and elsewhere, contain identical species with those now growing in England.

From what has been already brought before our notice it is clear that Araucarias, Pines, Cycads, Zamias, and other exogenous plants now growing, have their generic representatives as early as the Secondary ages. The persistence of a species through more than one geological period can seldom be traced; gaps intervene, and it is only indirectly that the changes which have taken place on the earth's surface can be determined, the evidences being too frequently rendered obscure by the superincumbent

beds, or placed altogether beyond our reach in the depths of the sea. The fact that the Cretaceous beds of Dorsetshire rest unconformably on the beds below shows that a great interval of time elapsed between the deposition of the two series, and accounts for the dissimilarity of their faunas. There are instances, however, where the chain of life is unbroken, and uninterruptedly carried on, although accompanied by the continual appearance of new forms.

NOTE.-The Geology of the County of Dorset is illustrated by the following works published by the Geological Survey of England. Maps on a scale of one inch to a mile, Sheets, 15, 16, 17, 18, 21, 22. Horizontal Sections, Sheets 19, 20, 21, 22 and 56. Vertical Sections, Sheet 22.

DRAINAGE.

A.

The Axe or Exe, which rises at Axnoll near Cheddington, is joined in the early part of its course at East Swillets, near Seaborough, by a tributary originating from the drainage of Lewesdon Hill, also by another from the western side of the same range, both of which after uniting pass through Broad Windsor and enter the main stream on its left bank at Axe near Wayford, where a third tributary from springs below Shave Lane Hill, one of the high cretaceous outliers which form the picturesque features of this attractive part of Dorsetshire, feeds it on its right bank.

Pillesdon Hill furnishes a streamlet, which after pursuing a northerly direction passes about a mile below Thorncombe, and joins the Axe near Winsham; several small rills flows into the main stream between this and the county border.

The Birt rises on the north side of Beaminster from springs udner White Sheet Hill, receiving the Simene from the hills above Symondsbury, between the town of Bridport and the harbour. The Asker from springs near Askerswell, which runs in a westerly direction to its junction with a considerable tributary at Long Loders, is fed by three rivulets, one rising above the marshes of Witherston, another from the base of Eggardon Hill, both uniting at Milton, and the third, which rises at or near Hook Park, joins them about a mile lower down.

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