Page:Quarterly Journal of the Geological Society of London, vol. 31.djvu/87

Rh IN THE ISLE OF PORTLAND AND ABOUND WEYMOUTH. 41 It is from 10 to 15 feet thick, and of a red and ochreous colour, but it weathers white. The matrix is a sandy loam and clay. Nine tenths of the gravel consist of well-rolled chalk flints ;i and the other tenth consists, in the order of their relative abundance, of : — 1, large and small white quartz and red quartz pebbles ; 2, subangular frag- ments of Portland flint; 3, chert and ragstone of the Greensand (some of the latter in blocks of considerable size ; one was 5| x 2| x 1 feet) ; 4, small subangular fragments of red porphyry ; 5, jasper ; and 6, a few small fragments of worn shelly limestone (Forest Marble ?). In places the gravel is much disturbed. The pit from which the above collection was obtained, is within 50 or 60 feet of the summit of Blackdowii (790 feet). The gravel is probably of older date even than the mammaliferous drift of Portland, and may belong to some part of the Glacial period. In none of these beds of gravel could I find either bones or shells ; but the remains of the elephant (Elephas primigenius 1 ?) have been found in a low-level drift (a, in Map, PI. I.) at Radipole, probably that which follows the course of the small stream, and was noticed by Dr. Buckland as being of some extent in the valley near Upway ; but no section of it was exposed at the time of my visit. A low- level valley-gravel also occupies the small Abbotsbury valley ; and a trail of gravel extends over the hill north of it and on the lower slopes of the Upway valley. Capping the high chalk ranges of Upton, the White Nore, and Abbotsbury, is a thick bed of perfectly angular sharp chalk-flints in a reddish clay reposing on a deeply indented surface of chalk, while a similar angular drift composed of fragments and masses of chert and ragstone cap the Upper- Green sand hills north of Abbotsbury. It is not, however, my intention to describe this or No. 8 further at present ; I merely refer to them as having been the storehouses whence much of the later drift-beds have been supplied. Calcareous Tufa Deposit. The raised beach on the east cliff is often cemented by carbonate of lime into a compact conglomerate. It also forms in places detached porous masses of tufa of considerable size, and fills up the interstices of the Purbeck debris. It is newer than the angular debris ; for in a section on the cliff near the lower lighthouse the fol- lowing is the order of superposition : — Tufa full of recent land-shells 1^ foot. Brown loam with angular debris 2 feet. Broken surface of Purbeck, with traces of beach. This tufa is apparently due to some springs which still occasionally issue on the slope of the hill a short distance inland from the beach, and which formerly gave off a greater volume of water than at present. Concluding Remarks. The study of the chronological relation of these deposits is a subject of much interest As before mentioned, Portland, with its capping