Page:Quarterly Journal of the Geological Society of London, vol. 31.djvu/97

Rh IN THE ISLE OF PORTLAND AND AROUND WEYMOUTH. 51 in the neighbourhood of Weymouth, the evidence is not very clear. Judging from the levels of these beds, they may probably be referred to different periods, extending from one shortly subsequent to the elevation of the anticlinal axis, to the one when the streams had obtained their present position and present level. Thus the small patch capping the hill beyond Preston may be the oldest (&") ; the patch between Chickerel and Portisham, and those on the hills near Osmington Mills, and which consist chiefly of large chalk-flints, may be the next (&') ; those above Badipole and the Portland Ferry, third ; while that in which the remains of the mammoth have been found is confined to the low-level beds of Eadipole and is the last (a). But the most anomalous mass is that between "Weymouth and Chickerel. It is composed, as before observed, almost entirely of subangular fragments of Greensand chert. The lie of the land, which intercepts communication with the Abbotsbury hills, and the presence of the more composite drift both to the north and south, lead me to suppose that this Greensand drift may have been derived rather from the district of the White Nore before the excavation of Weymouth Bay than from that of Abbotsbury ; but I must leave this question open. It does not seem connected with any river-gravel. The drift between Wyke and the Perry, where we get Greensand chert, chalk-flints, and Portland ohertmixed, may possibly be assigned to the same age. On the other hand, regarding the drift in the Upway valley and at Eadipole as a low-level valley gravel, that on the hill east of Eadipole, which contains an abundance of Tertiary debris together with chalk-flints brought down from the hills at the head of the Upway valley, may be a high-level gravel of the same river-system. Such, briefly, appear to be the very remarkable series of pheno- mena which, at a comparatively recent geological time, have given form and shape to the district round Weymouth. Carrying our view back to the latter part of the Glacial Period, before the present valley-systems or even some of our plains were elaborated, a broad tract of Chalk, bounded in places by Greensand, and capped by Ter- tiary beds and older gravels, rose inland ; and with these the Purbeek and Portland beds were brought into level juxtaposition by and along the great line of fault running westward and eastward nearly midway between Dorchester and Weymouth. From that district the surface of the country sloped gradually to the south end of Portland ; and over this surface, which then bridged over the plain of Weymouth, streams, originating in the Chalk, Greensand, and Tertiary district, flowed southward to the Channel. It was one of these streams which, passing over Portland, rolled down to that island pebbles derived from those several newer formations, while the floods and ice of winter carried down the larger Sarsen-stone boulders also so common in the same fluviatile bed, and entombed the remains of the elephant, horse, &c, then living in that area. At this time the line of coast extended, much as it does now, but with fewer and deeper bays, from the shores of Cornwall, passing close to Plymouth, touching the headlands of Berry Head, Start Point, and e2