Drift Surface Research Articles

The Damping of Water Waves by Surface Films

Measurements have been made of the stilling of small water ripples by surface :films of cetyl alcohol. The damping is considerable and is somewhat in excess of that predicted by existing theories. Imperfections in the ripples induce a directed surface drift (surface mass transport), and it is possible that this is indirectly responsible for the extra damping. Under natural conditions surface films not only impede the formation of small waves but they are also very effective in damping them out.

Pleistocene geology of the country around Bromsgrove

The Pleistocene Deposits of a triangular area in Worcestershire, enclosed by the villages of Romsley, Barnt Green and Upton Warren, are divided into Older and Newer Drifts. The Older Drifts are of higher level and consist of gravels below and a boulder clay above. The Newer Drifts are valley terraces deposited in the valleys, cut below the Older Drift level. Five such terraces are recognised and they are correlated with the terrace stages established by Professor Wills for the Severn Valley. Finally, the nature of the sub-Older Drift surface is described. This shows a deep, buried channel which is interpreted as an ice marginal overflow channel.

Note on wind drift in a channel in the presence of tidal currents

In waters such as those surrounding the British Isles, wind currents appear as perturbations superimposed on the tidal currents. In treating this problem, it is assumed that the drift velocity is small compared with the amplitude of the tidal current. In this case, if the instantaneous value of the bottom friction is proportional to the square of the instantaneous velocity, the non-periodic component of friction, averaged over a tidal period, is linearly proportional to the drift velocity. It is assumed that the water is homogeneous and that, above a skin-friction layer close to the bottom, the eddy viscosity is constant with depth. In the steady state, the drift current due to a given wind stress is reduced in the presence of tidal currents. Steady-state solutions, involving the elevation of the surface as well as the currents, are given for a channel of uniform width and depth, a uniformly convergent channel and a non-uniform channel. Numerical calculations, based on the most probable estimates of wind stress, eddy viscosity and bottom friction available at present, are given for several particular cases. A discussion is given of their application to drift currents and surface gradients in the English Channel, a region in which it is proposed to carry out a programme of observations in the near future.

Geological Museum: Recent Acquisitions

AMONG the recent acquisitions of the Geological Museum is a large geological relief model of the London basin, measuring about 10 ft. by 5 ft. This is constructed on a scale of 1 in. to a mile, vertical heights being exaggerated about six times, and it includes an area extending from Foulness in the east to the Vale of White Horse in the west, and from Baldock in the north to Leith Hill in the south. The model illustrates clearly the main synclinal structure of the London basin, from the chalk rocks of which London draws so much of its water supply. Details of this structure of the solid rocks are accentuated by the colouring of drift and other surface deposits by various shades of stipple superimposed on the solid geology. A second relief model just placed on exhibition illustrates the glacial lakes of Cleveland, on a scale of 1 in. to a mile. This reconstruction, which is based on the work of the late Prof. P. F. Kendall, shows the glaciers, ice-dammed lakes, and drainage system of the Cleveland area at the time of the maximum extension of the Pleistocene ice-sheets. Among the dioramas recently added to the displays is one of an Anglo-Iranian oil-field, presented by the Anglo-Iranian Oil Co. This is the second experiment in a type of diorama in which the foreground is cut away to a depth of several thousand feet to show the geology. Two diamonds of unusual crystal form from Atian Kama, Akim, Gold Coast, have been given by Mr. G. P. Ashmore. Some five hundred varieties of marble used in decorative work in Western Europe are now being exhibited.

On two river channels buried under drift, belonging to a period when the land stood several hundred feet higher than at present

Remarks on the Drift Deposits. —The drift and other surface deposits of the country have chiefly been studied from sections observed on the banks of streams, railway cuttings, ditches, foundations of buildings, and other excavations. The great defect of such sections is that they do not lay open a sufficient depth of surface. They may no doubt represent pretty accurately the character and order of the more recent deposits which overlie the boulder-clay, but we are hardly warranted in concluding that the succession of deposits belonging to the earlier part of the glacial epoch, the period of the true till, is fully exhibited in such limited sections. Suppose, for example, the glacial epoch proper—the time of the lower boulder-clay—to have consisted of a succession of alternate cold and warm periods; there would, in such a case, be a series of separate formations of boulder-clay; but we could hardly expect to find on the flat and open face of the country, where the surface deposits are generally not of great depth, those various formations of Till, lying the one superimposed upon the other. For it is obvious that the till formed during one ice period would, as a general rule, be either swept away, or re-ground and laid down by the ice of the succeeding period. If the very hardest rocks could not withstand the abrading power of the enormous masses of ice which passed over the surface of the country during the glacial epoch, it is hardly to be expected that