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Show 172 OLDER PLIOCENE rER10D. [Ch. XIII. consist of sand, gravel, and blue or brown marl-the shells imbedded in the sand and marl being, for the most part, broken nnd sometimes finely comminuted. In a few spots we find the deposit in the form of a soft stratified rock, composed almost entirely of corals, sponges, and echini *, an assemblage of species which probably lived in a tranquil sea of some depth. In other parts of our coast it consists of alternations of sand and shingle, destitute of organic remains, and more than 200 feet in thickness, as in the Suffolk cliffs, between Dunwich and Yarmouth. In others, we meet with an enormous mass, more than 300 feet in thickness, of sand, loam, and clay, containinO' 0 bones of terrestrial quadrupeds and drift wood, sometimes stra-tified regularly, at nthers consisting of a confused heap of rubbish, in which fragments of the chalk and its flints are imbedded in a chall{y marl. In this aggregate are also found many fragments of older rocks, the septaria of the London clay, together with ammonites, vertebrre of ichthyosauri, and other fossils from parts of the oolitic series. It has been questioned whether all the above-mentioned beds can be considered as belonging to the same era. The subject may admit of doubt, but after examining, in 1829, the whole line of coast of Essex, Suffolk, and Norfolk, I found it impossible to draw any line of separation between the different groups. Each seemed in its turn to pass into another, and those masses which approach in character to alluvium, and contain the remains of terrestrial quadrupeds, are occasionally intermixed with the strata of the crag. There are, however, lacustrine deposits overlying the crag, which probably belong to a distinct zoological period. These are found in small cavities, which must have existed on the surface of the crag after its elevation, and which formed small lakes or ponds wherein recent fresh-water testacea were included in loamy strata. (See wood-cut, No. 30, c.) Relative position.-The crag is seen to rest on the chalk and on the London clay, but usually on the former. The strata "' R, Taylor, Geol. of E!~-l:lt Norfolk. Ch. XIII.] CRAG OF ENGLAND. 173 are in great part horizontal, or slightly undulating; but at some points they are much disturbed, especially where several masses of chalk appear to have been protruded from below. The annexed section may give a general idea of the manner in which the crag may be supposed to rest on the chalk as we pass from the Norfolk cliffs, at rrrimmingham, into the interior, where the country rises gradua11y. No.30. E ~~ a, Chalk. b, Crag. c, Lacustrine deposit. D, T1·immingham beacon. E, Interior and higher parts of Norfolk*· The outline of the surface of the subjacent chalk, in this section, is imaginary, but is such as might explain the relations of those protruded masses, three of which appear in the cliffs near Trimmingham, and which some geologists have too hastily assumed to be unconnected with the great mass of chalk below. We shall treat of these presently, when we describe the distmbances which the crag appears to have suffered since its original deposition. In the interior, at E, there is a thick covering of sand and gravel upon the chalk, having the characters of an alluvium, partly, perhaps, marine, and partly terrestrial, and which seems to pass gradually in this district into the regular marine strata of the crag. . ~orms of stratification.-In ' almost every formation the indlVldual strata are rarely persistent for a o-reat distance the superior and inf:rior planes being seldom p~ecisely parall:l to ca~h other; and 1f the materials are very coarse, the beds ofren tlnn out if we trace them for a few hundred yards. There are also many cases where all the layers are oblique to the general th ~ Tit is section is compiled principally from one by Mr. Murchison the others in IS chapter are from drawings by the Author. ' |