idea of creating a photographic history of pioneer life in Nebraska. Between 1886 and 1912, he produced nearly 3,500 glass plate negatives; over 1,800 of these were taken in Custer County, and over 1,500 show sod houses. Butcher's photographs are now owned by the Nebraska State Historical Society. Sod construction In constructing a sod house, a site had to be chosen that was close to good sources of sod. All prairie grasses were not alike for purposes of construction sod; the best were those with a strong and dense root network to hold the blocks together. Preferred species included buffalo grass (Bouteloua dactyloides), slough grass (Spartina pectinata), and big bluestem (Andropogon gerardi). At the house site, the grass was removed. Often, the soil was excavated one to two feet () below ground level; this reduced the height of the walls, and thus the amount of sod that had to be cut. The ground that would form the house floor was moistened and then tamped with a fencepost to flatten and harden it. Footings were rarely laid, due to the cost or unavailability of material. Before the sod blocks were cut, the grass was mown short or burned off. At times, the surface was scored with a cutter or disc; the blocks could then be removed with a spade. This approach, however, tended to produce rough and non-uniform blocks, which complicated the task of laying them in even courses. Blocks could also be cut with a plow. An ordinary plow could be used, given considerable skill and care on the part of the operator; however, the mouldboard tended to turn over and break up the blocks; even if intact blocks were produced, they were generally not of uniform thickness. In the late 19th century, a modified plow designed specifically for sod cutting was invented: this "grasshopper plow" replaced the mouldboard with a set of adjustable rods, which allowed the operator to cut a uniform strip of sod three to six inches () deep and wide. This strip could then be cut into blocks. The dimensions of these depended, among other things, on the strength of the builder—the blocks were dense, and had to be sized so that the builders could lift them. Typical blocks cut with a grasshopper plow might measure four inches () deep by wide by long. In building the walls, the sod blocks were laid one course at