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Show 182 OLDER PLIOCENE PERIOD. l Ch. XIII. of England, which may, therefore, have be~n fo~·med when the testacea of the older Pliocene period were m existence. Upon the whole, we may. imagine the crag strata to beat· a great resemblance to the formations which may now be in progress in the sea between the British and Dutch coasts,-a sea for the most part shallow, yet having here and there a depth of 50 or 60 fathoms, and where strong tides and currents prevail; where shells, also, and zoophytes abound, and where matter drifted from wasting cliffs must be thrown down in certain receptacles in the form of sand, shingle, and mud. In conclusion we may observe that the history of the crag requires further elucidation, and the author is by no means satisfied with the sketch above given; but as the country is so accessible and the formation so interesting both in its structure and zoological characters, it is hoped that these remarks may excite curiosity and lead to fuller investigation. Sheppey.- Ramsgate.- Brighton.-Deposits have lately been observed by Mr. Crow * resting on the London clay, in the Isle of Sheppey, at the height of 140 feet above the sea, and by Captain Kater at Pegwell Bay, near Ramsgate, at the height of a few yards, and by Mr. Mantell, in the cliffs near Brighton, all containing recent marine shells. But as there are only five or six species yet discovered in these localities, we cannot decide, till we obtain further information, whether these strata belong to the crag or to a more recent formation. * Of Christ Church College, Cambridge. CHAPTER XIV. Volcanic rocks of the older Pliocene period-Italy-Volcanic region of Olot in Catalonia-Its extent and geological structure-Map-Number of conesScoriw- Lava currents-Ravines in the latter cut by water-Anci~nt alluvium underlying lava-Jets of ail' called 'Bufadors '-Age of the Catalonian volcanos uncertain-Earthq11ake which destroyed Olot in 1421-Sardinian volcanos- District of the Eifel and Lower Rhine-Map-Geological structure of the country-Peculiar characteristics of the Eift:Jl volcanos-Lake cratersTrass- Crater of the Roderberg-Age of the Eifel volcanic rocks uncertainBrown coal formation. VOLCANIC ROCKS OF THE OLDER PLIOCENE PERIOD. Italy.- IT is part of our proposed plan to consider the igneous as well as the aqueous formations of each period, but we are fat· from being able as yet to assign to each of the numerous groups of volcanic origin scattered over Europe a precise place in the chronological series. We have already stated that the volcanic rocks of Tuscany belong, in great part at least, to the older Pliocene period,-those for example of Radicofani, Viterbo, and Aquapendente, which have been chiefly erupted beneath the sea. The same observation would probably hold true iu regard to the igneous rocks of the Campagna di Roma. But several other districts, of which the dates are still uncer~ain, may be mentioned in this chapter as being possibly refernble to the period now under consideration. It will at least be useful to explain to the student the points which require eluci~ation before the exact age of the groups about to be described can be accurately determined. Volcanos of Olot, in Catalonia.-! shall first direct the reader's attention to a district of extinct volcanos in the north of Spain, which is little known, and which I visited in the summer of 1830 . . The whole extent of country occupied by volcanic products lU Catalonia is not more than fifteen geographical miles from |
