The lower portion of the inner slope to a height of 16 feet below the crest of the spillway , to be paved with stone , 18 inches thick , laid dry , upon 12 inches of broken stone , and on the upper part of the slope to a height 12 feet above the crest of the spillway , the paving stone was to be two feet thick , upon 18 inches of broken stone . The core wall in the centre of the embankment was to be four feet higher than the crest of the spillway , six feet wide at the top and increasing to 18 feet at a depth of 136 feet , then same width to the base .

The core wall was to be 200 feet high at the junction with the stone dam and 90 feet high at a gate house that is built in the embankment , 290 feet from the stone dam . The high end of the core wall had been built in a wide pit , that was a necessary excavation for the end of the stone dam , which was 164 feet wide at the base , while the core wall was but 18 feet at its base . The slope of this pit extended southerly along the line of the wall for a distance of 150 feet , thus the core wall at its highest end was not built in a narrow trench below the surface of the ground , as is usual in ordinary cases .

The bed rock on the north side of the valley is gniess and the structure is founded upon it for a length of 1,200 feet . The character of the rock then changes abruptly from gniess to lime stone and this extends southerly beyond the end of the structure .