It was thought possible at the Tabeaud dam to counteract the tendency of the face puddle to slough off into the reservoir by use of a broken stone facing of riprap. This covering will protect the puddle from the deteriorating effects of air and sun whenever the water is drawn low and also resists the pressure at the inner toe of the dam. Percolation and Infiltration. The earlier authorities on the subject of percolation and infiltration of water are somewhat conflicting in their statements, if not confused in their ideas. We are again impressed with the importance of a clearly defined and definite use of terms. The temptation and tendency to use language synonymously is very great, but it is unscientific and must result in confusion of thought. Let it be observed that _filtration_ is the process of mechanically separating and removing the undissolved particles floating in a liquid. That _infiltration_ is the process by which water (or other liquid) enters the interstices of porous material. That _percolation_ is the action of a liquid passing through small interstices; and, finally, that _seepage_ is the amount of fluid which has percolated through porous materials. Many recent authorities are guilty of confusion in thought or expression, as will appear from the following: One says, for instance, that a rock is water-tight when non-absorbent of water, but that a soil is not water-tight unless it will absorb an enormous quantity of water. This would seem to indicate that super-saturation and not pressure is necessary to increase the water-tightness of earth materials. Again, in a recent discussion regarding the saturation and percolation of water through the lower half of a reservoir embankment, it was remarked, that the more compact the material of which the bank is built, the steeper will be the slope of saturation. Exception was taken to this, and the statement made, that _with compact material_, the sectional area of flow is larger below a given level with porous material, and as the bank slope is one determining factor of the line of saturation, this line tends to approach the slope line; while with porous material in a down-stream bank, the slope of saturation is steeper and the area of the flow less. In reply to this, it was said, that it is obvious that if the embankment below the core wall is built of material so compact as to be impervious to water, no water passing through the wall will enter it, and the slope of saturation will be vertical. If it be less compact, water will enter more or less according to the head or pressure, and according to its compactness or porosity, producing a slope of saturation whose inclination is dependent on the frictional resistance encountered by the water. And the bank will be tight whenever the slope of saturation remains within the figure of the embankment. Further,