During the great drought in 1929 there came to light at Gouthwaite Reservoir in Nidderdale three sites of Upper Palaeolithic industry. In that summer the level of the water became so low that the reservoir was less than half full, thus affording an opportunity for field work. The Pleistocene deposit exposed consists of a stiff yellow clay covered with sand and gravel along the banks of the reservoir, washed out by the action of the water in rough weather, from the lateral moraines. This clay is exposed in many places when the water has fallen 4 ft. below ordinary level, and it is on this horizon that Upper Palaeolithic man apparently lived. A complete geological section across the valley in this part does not exist, but sections of trial holes were made when the construction of the dam at Gouthwaite was being undertaken and for the copies of these sections I am indebted to Mr. E. Tillotson of Leeds University. The dam is actually built at the upper end of the last, and best preserved, terminal moraine in the valley. From the section it appears that the yellow clay stretches right across the valley, forming the uppermost stratum of the terminal moraine. This being so, and if this was the horizon on which the inhabitants lived, then the terminal moraine must have been cut through by the river action, otherwise the horizon on which the Upper Palaeolithic implements are found would have been under water and not habitable.