I. Introduction. The section described in this paper has been exposed in the course of construction of a reservoir for the Grangemouth Town Council, near North Third farm steading, 4½ miles S.W. of Stirling, and about 3 miles W. of Bannockburn. The puddle trench has been excavated in an E.-W. direction along the centre line of a proposed embankment, which, when completed, will dam back the upper waters of the Bannock Burn. The raison d'etre of a puddle trench may readily be grasped by a glance at Fig. 1. Although the earthwork embankment built across the valley might itself be impervious to water, the pressure due to the water in the reservoir would force the water along the previous subsoil and strata underlying the embankment. To prevent this leakage, which would not only be a source of waste but a positive menace to the stability of the embankment, a trench is sunk along the centre-line of the proposed embankment until a solid, impermeable stratum is reached, or at least to a depth at which no serious leakage from the reservoir is expected. The trench is then packed with “puddled clay,” forming an impermeable wall through the opener strata under the embankment. The puddled clay is continued right up through the heart of the embankment, rendering that watertight also. The figure below shows the method of construction. The North Third puddle trench is about 340 yards long, with a width of about 15 feet, and a maximum This 250-word extract was created in the absence of an abstract