Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/147

Rh LATER TERTIARY GEOLOGY OF EAST ANGLIA. 109 sides of each valley the Middle Glacial is exposed beneath it by the valley-denudation. In the Brett valley the London-clay floor is ex- posed as far up as above Hadleigh ; but although some traces of the Red Crag have been found in it by the members of the Geological Survey, the Contorted Drift does not show itself as coming out on the lower slope of this valley, unless a brick-earth occurring at Layham * belongs to that drift. In the Boxford valley, however, the Contorted Drift is exposed at Boxford brick-kiln in several sections, in one of which we found it overlain by the Upper Glacial clay with a slight thickness of Middle Glacial gravel between them. Below Boxford for some miles the Contorted Drift seems to occupy the valley-bottom ; and on the summit of the tableland dividing this valley from that of the Brett, and nearly midway between them, we came, at a place called " Coyts Tye," upon a deep excavation of laminated brick-earth, which we regard as most probably the Contorted Drift. It is, of course, possible that this brick-earth may be Postglacial, and occupy a hollow in the Upper Glacial clay which covers the country all round ; but the depth to which it was excavated (upwards of 30 feet), and the position which it occupies on the water-parting of the district, militate against this view. Assuming that our view as to the identity of this brick -earth with the Contorted Drift is well founded, it indicates, in connexion with the exposures in the valley at Boxford, that the excavation of these two valleys was of interglacial origin, and precisely analogous to what we have shown as obtaining in the caso of the valleys of the Orwell and Deben estuaries. Section XXII. shows what, accord- ing to our view, these exposures indicate. Fig.23. — Section XXII., from the Boxford Valley to the Brett Valley. (Length 4 miles. Vertical scale 17£ times the horizontal.) Valley of the Brett. Boxford Brick-pit at N". end of Brick-pits. Coyts Tye. Hadleigh. Keferences as in figs. 21 & 22. We have not been able to detect the presence of the Contorted Drift in Essex beyond Bulmer, near Sudbury, where we found what we regarded as that deposit overlain by 11 feet of Middle Glacial in a pit half a mile north-east of the church ; but, from some sections 1869, to be in the Woolwich beds and London clay ; but Mr. Whitaker informs us that the Survey regard them as being in a Glacial bed. They are overlain at one place by the Upper Glacial.
 * The excavations at Layham seemed to us, when we examined them in