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Show 316 ISLAND LIFE. (PART II. in the clay, without anything like a prevalent direction. The trunks varied from six inches to upwards of two feet in diameter. Much of the wood was found to have a reddish or bright pink hue, when fresh surfaces were exposed. Some of it, as well as many of the twigs, had almost become a sort of ligneous pulp, while o~her examples were firm, and gave a sharp crackling Round on be111g broken. Several large stumps projected above the clay in a vertical direction, and sent roots and rootlets into the soil in all directions and to considerable distances. It was obvious that the movement by which the submergence was effected had been so uniform as not to destroy the approximate horizontality of the old forest ground. One fine example wa.s noted of a large prostrate trunk having its roots still attached some of them sticking up above the clay, while others wer~ buried in it. Hazelnuts were extremely abundant-some entire others broken, and some obviously gnawed .... It has bee~ s:ated that the forest area reached the spring-tide low-water hne ~ hence as the greatest tidal range on this coast amounts t~) eighteen feet, we are warranted in inferring that the subSidence amounted to eighteen feet as a minimum, even if we su~pose that some of the trees grew in a soil the surface of whiCh was not above the level of high water. There is satisfactory ev~dence that in Torbay it was not less than forty feet, and that 111 Falmouth Harbour it amounted to at least sixt _ seven feet." 1 Y . On the coast of the Bristol Channel similar deposits occur as well as alon?' mu~h of the coast of Wales and in Holyhead Harbour. It IS believed by geologists that the whole Bristol Ch~nnel was, at a comparatively recent period, an extensive pla111, thr~ugh which flowed the River Severn; for in addition to the evidence of submerged forests there are on the coast of Glamorganshire numerous caves and fissures in the face of h · h l'ff: . Ig se~ c I s, 111 one of which no less than a thousand antlers of the re111deer were found, the remains of animals which had been devo~red there by bears and hyrenas; facts which can only be expla111ed by the existence of some extent of dry land stretching seaward from the present cliffs, but since submerged and washed I Geological Magazine, 1870, p. 165. CHAP. XVI.] THE DRI'l'ISH ISLES. 317 away. This plnin may have continued down to very recent times, since the whole of the Bristol Channel to beyond Lundy Island is under twenty-five fathoms deep. In the east of E~gland we have a similar forest-bed at Cromer in Norfolk; and 111 the north of Holland an old land surface has been found fifty-six feet below high-water mark. . Buried River Channels.- Still more remarkable are the buned river channels which have been traced on many parts of our coasts. In order to facilitate the study of the glacial deposits of Scotland, Dr. James Croll obtained the details of about 250 bores put down in all parts of the mining districts of Scotland for the purpose of discovering minerals.1 These revealed the interesting fact that there are ancient valleys and river channels at depths of from 100 to 260 feet below the present sea-level. These old rivers sometimes run in quite different directions from the present lines of drainage, connecting what are now distinct valleys; and they are so completely filled up and hidden by boulder clay, drift, and sands, that there is no indication of their presence on the surface, which often consists of mounds or low hills more than 100 feet high. One of these old valleys connects the Clyde near Dumbarton with the Forth at Grangemouth, and appears to have contained two streams flowing in opposite directions from a watershed about midway at Kilsith. At Grangemouth the old channel is 260 feet below the sea-level. The watershed at Kilsith is now 160 feet above the sea, the old valley bottom being 120 feet deep or forty feet above the sea. In some places the old valley was a ravine with precipitous rocky walls, which have been found in mining excavations. Dr. Geikie, who has himself discovered many similar buried valleys, is of opinion that "they unquestionably belong to the period of the boulder clay." We have here a clear proof that, when these rivers were formed, the land must have stood in relation to the sea at least 260 feet higher than it does now, and probably much more ; and this is sufficient to join England to the continent. Supporting this evidence, we have freshwater or littoral shells found at great depths off our coasts. Mr. Godwin Austen records the dredging I T1·ansactions of the Edinburgh Geological Society, Vol. I. p. 330. |