A typical crib dam, filled with stone, is shown in section in the diagram, and the half-tone illustration shows such a dam in course of construction. The first bed of timbers should be laid on hard-pan or solid rock in the bed of the stream parallel to its flow. The second course, across the stream, is then begun, being spiked home by means of rods cut to length and sharpened by the local blacksmith, from 3/4-inch Norway iron. Hemlock logs are suitable for building the crib; and as the timbers are finally laid, it should be filled in and made solid with boulders. This filling in should proceed section by section, as the planking goes forward, otherwise there will be no escape for the water of the stream, until it rises and spills over the top timbers. The planking should be of two-inch chestnut, spiked home with 60 penny wire spikes. When the last section of the crib is filled with boulders and the water rises, the remaining planks may be spiked home with the aid of an iron pipe in which to drive the spike by means of a plunger of iron long enough to reach above the level of the water. When the planking is completed, the dam should be well gravelled, to within a foot or two of its crest. Such dams are substantial, easily made with the aid of unskilled labor, and the materials are to be had on the average farm with the exception of the hardware. [Illustration: Cross-section of a rock and timber dam] This dam forms a pond from which the race draws its supply of water for the wheel. It also serves as a spillway over which the surplus water escapes. The race should enter the pond at some convenient point, and should be protected at or near its point of entrance by a bulkhead containing a gate, so that the supply of water may be cut off from the race and wheel readily. The lay of the land will determine the length and course of the race. The object of the race is to secure the required head by carrying a portion of the available water to a point where it can escape, by a fall of say 30° to the tailrace. It may be feasible to carry the race in a line almost at right angles to the stream itself, or, again, it may be necessary to parallel the stream. If the lay of the land is favorable, the race may be dug to a distance of a rod or so inshore, and then be permitted to cut its own course along the bank, preventing the water escaping back to the river or brook before the site of the power plant is reached, by building suitable retaining embankments. The race should be of ample size for conveying the water required without too much friction. It should end in a flume constructed stoutly of timbers. It is from this flume that the penstock draws water for the wheel. When the wheel gate is closed the water in the mill pond behind the dam, and in the flume itself should maintain an approximate level. Any surplus flow is permitted to escape over flushboards in the flume; these same flushboards maintain