446 J. C. Ma7isel-Pleyclell~ Geology of Dorset. 



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 sub-aerial deposits in the county ; 

 the most remarkable of these is at Blashenwell, between Corfe Castle 

 and Kingston, where a tufaceous deposit about 10 feet thick, con- 

 taining 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 lime 

 held in solution in the water which passed through it. 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 by 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 Kimmeridge Cliffs, showing 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 marine organisms 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 geo- 

 logical period is now incontestably established.^ The Devonian 

 epoch presents Conifercs, Sigillarice, 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 Oycadecs compared with the diminishing 

 ratio of Equisetacece 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 Crustacea, 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 grass- 

 hoppers. 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 re-appear between intervals of several 



^ "When visiting the Isle of Portland in August last in company with Mr. Prestwich, 

 that gentleman pointed out to me undoubted proofs of Glacial action which had 

 hitherto escaped notice. — J. C. M.-P. 



"^ See paper by H. Woodward on the Carboniferous and other Old Land Surfaces, 

 Geol. Mag., 1871, Vol. VIII., p. 492. 



