represented, is 24 feet in height. Some of the layers in b, b, are composed of pebbles, and these alternate with thin beds

No. 40.

Section east of Sherringham, Norfolk.

a, Sand, loam, and blue clay. b, b, Sand and gravel. c, Twisted beds of loam. of loose sand. The whole set must once have been horizontal, and must have moved in a mass, or the relative position of the several parts would not have been preserved. Similar appearances may, perhaps, be produced when chasms open during earthquakes and portions of yielding strata fall in from above and are engulphed.

Protruded masses of chalk.-But whatever opinion we may entertain on this point, we cannot doubt that subterranean

Side view of a promontory of chalk and crag, Trimmingham, Norfolk.

a, Gravel and ferruginous sand, rounded and angular pieces of chalk flint, with

some quartz pebbles, 3 feet.

b, Laminated blue clay, 8 feet.

d, Dark blue clay with fragments of marine shells, 6 feet.

e, Yellow loam and flint gravel, 3 feet.

g, Sand and loam, 12 feet.

c, Yellow sand, 1 foot 6 inches.

f, Light blue clay, 1 foot.

h, Yellow and white sand, loam, and gravel, about 100 feet.

movements have given rise to some of the local derangements in this formation, particularly where masses of solid chalk pierce, as it were, the crag. Thus, between Mundesley and Trimmingham we see the appearances exhibited in the accompanying view (No. 41). The chalk, of which the strata are highly inclined, or vertical, projects in a promontory, because it offers more resistance to the action of the waves than the tertiary beds which, on both sides, constitute the whole of the cliff. The height of the soft crag strata immediately above the chalk is, in this place, about 130 feet. Those which are in contact (see the wood-cut) are inclined at an angle of 45°, and appear more disturbed than in other parts of the cliffs, as if they had been displaced by the movement by which the chalk was protruded.

Very similar appearances are exhibited by the northernmost of the three protuberances of chalk, of which a front view is given in the annexed diagram. It occupies a space of about 100 yards along the shore, and projects about 60 yards in advance of the general line of cliff. One of its edges, at c, rests upon

b. Gravel, of broken and half-rounded flints. d. Sand and yellow loam.

the blue clay beds of the crag, in such a manner as to imply that the mass had been undermined when the crag was deposited, unless we suppose, as some have done, that this chalk is a great detached mass enveloped by crag. For,

as one of the Needles', or insulated rocks of chalk, which projected 120 feet above high water-mark, at the western extremity of the Isle of Wight, fell into the sea in 1772 *, so a pinnacle of chalk may have been precipitated into the tertiary sea, at a point where some strata of the crag had previously accumulated. The beds of flint and chalk in the above diagram appear nearly horizontal, but they are in fact highly inclined inwards towards the cliff. The rapid waste of the Norfolk coast might soon enable us to understand the true position of this mass, if observations and drawings are made from time to time of the appearances which present themselves.

Perhaps it may be necessary to suppose, that subterranean movements were in progress during the deposition of the crag, and the extraordinary dislocations of the beds, in some places, which in others are perfectly regular and horizontal, may be most easily accounted for by introducing an alternate rise and depression of the bed of the sea, such as we know to be usually attendant on a series of subterranean convulsions. Several of the contortions may also have been produced by lateral move

ments.

Passage of marine crag into alluvium.-By supposing the adjoining lands to have participated in this movement, we may explain the origin of those masses of an alluvial character which contain the detritus of many rocks, the bones of land animals and of drift timber, which were evidently swept down into the sea. The land-floods which accompany earthquakes are, as we have seen, capable of transporting such materials to great distances †, and, as part of these alluviums must be left somewhere upon the land, we may expect to find, on exploring the interior, a gradual passage from the terrestrial alluvium to that which was carried down into the sea, and which alternates with marine beds.

The fossil quadrupeds imbedded in the crag appear to be the same as those of a great part of the alluviums of the interior Vol. i. chap. 25.

* Dodsley's Annual Register, vol. xv. p. 140.

of England, which may, therefore, have been formed when the testacea of the older Pliocene period were in existence.

Upon the whole, we may imagine the crag strata to bear 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.

Volcanic rocks of the older Pliocene period-Italy-Volcanic region of Olot in Catalonia-Its extent and geological structure-Map-Number of conesScoria-Lava currents-Ravines in the latter cut by water-Ancient alluvium underlying lava-Jets of air called Bufadors '-Age of the Catalonian volcanos uncertain-Earthquake which destroyed Olot in 1421-Sardinian volcanos-District of the Eifel and Lower Rhine-Map-Geological structure of the country-Peculiar characteristics of the Eifel volcanos-Lake craters-Trass-Crater of the Roderberg-Age of the Eifel volcanic rocks uncertain— Brown 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 far 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 in regard to the igneous rocks of the Campagna di Roma.

But several other districts, of which the dates are still uncertain, may be mentioned in this chapter as being possibly referrible to the period now under consideration. It will at least be useful to explain to the student the points which require elucidation before the exact age of the groups about to be described can be accurately determined.

Volcanos of Olot, in Catalonia.-I 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 in Catalonia is not more than fifteen geographical miles from