Some recent work by Dr. J. F. Nye on the calculation of the thickness of ice sheets has prompted the author to apply Nye’s formula to the Barnes Ice Cap in Baffin Island. A gravimetric survey of the southern lobe was carried out in 1950, and the data from four of the traverses have been used to calculate the variation of the shear stress on the bed. Some of the values obtained are exceptionally low, possibly explained by the fact that the lines of travel over the surface do not necessarily correspond to the lines of greatest slope or lines of flow. Only in one direction are the values relatively high, and it is concluded that there is a considerably greater movement of the ice in this direction. This conclusion is in agreement with observations on the ground.

The heat exchange takes place in two stages: (i) the atmospheric heat causes melting of the whole of the annual snow accumulation and leads to the formation of slush rivers; (ii) some of the melt water refreezes to form a new layer of ice superimposed on the original ice, which is warmed by the latent heat yielded to it. A theoretical estimate of the rate of formation of the superimposed ice, and of the temperature change in the original ice, is given, which agrees reasonably with the actual measurements. A rough measurement of the melt water run-off checks with the observations of ablation and superimposed ice. The total energy available for melting is estimated approximately from the meteorological observations; it underestimates the actual ablation. About 70 per cent of the total ablation energy (47 cm. water, total ablation) is disposed of as melt water that is discharged from the ice cap surface; the remainder goes as sensible heat to the low temperature ice.

The existence of high rock thresholds beneath the glaciers of Dronning Louise Land is established and examples are described. It is concluded that decrease in the height of the Greenland Ice Cap and the consequent emergence of the rock thresholds is the dominant factor in the final stages of recession of the glaciers of Dronning Louise Land. It is tentatively suggested that this process has more than local significance, and may be an important factor in the recent recession of the glaciers in other parts of east Greenland.

Contrary to prevailing opinions, the glaciers of south Patagonia have normally been stationary or have advanced during the last twenty years. Exceptions can be accounted for by a lag due to a long travel through narrow passes or by the lowering of waters in the terminal lake at the foot of a rocky cliff.

The distribution of temperature throughout an ice sheet has been considered, taking into account the influence of ice movement as well as other items previously considered, such as conduction, the geothermal outflow of heat and heat generated by ice movement. By making certain simplifying assumptions, a quantitative method of estimating the temperature distribution near the centre of an ice sheet has been put forward.

It is shown that even a small mean annual accumulation will have considerable effect on the temperature distribution in a large ice sheet. For a moderate rate of accumulation a substantial fraction of the total thickness of ice at the centre of a large ice sheet may be isothermal at the prevailing surface ice temperature. Under these conditions at some distance from the centre, the change in the surface ice temperature with elevation may produce a temperature gradient opposite to normal, that is the temperature falls with increasing depth below the surface, due to the outward movement of the ice. Observed temperature gradients on ice sheets fit the proposed hypotheses roughly, but it appears that climatic change should also be taken into account.

It is suggested that a rise from temperatures below melting point at the base of ice sheets may provide an explanation of the occasional catastrophic advances of certain glaciers.

It is suggested that both discontinuous shearing and continuous flow (creep) may coexist in one and the same glacier, provided the stress is high enough for the shear resistance to be reached. Experiments made in a tunnel in the Z’Mutt Glacier suggest that all the motion here observed was continuous, and also show that the viscosity is influenced by the stress conditions. A series of tests made by forcing a ball into the ice also enabled estimates of the viscosity and melting pressure to be made and emphasized the importance of melting in glacier flow.