There is but little indication of organic matter in the water of the large spring, though there is a slimy white deposit adhering to the bottom and sides, but the water is colorless, clear, and transparent. The excess of water, instead of overflowing the bank, escapes by numerous small fissures, from 10 to 20 feet down on the sides, especially on the side away from the bluff. In these lateral springs there is an abundance of green algæ, and a whitish scum, which seems to be detached from the bottom and to float to the surface. This has a slimy, granular feeling suggesting in a very marked manner hydrated silica. The mound is situated within about 200 feet of a limestone bluff, which rises perhaps 20 feet above the level of the spring. The natural inference would be that the harder material of the mound protected it from the erosion which carried away the rock in the valley of the Solomon on the south, and the rock between the spring and the bluff. Is it not possible however that the mound has been really made by the successive deposits from the spring? Although the mound is plainly stratified, this need not interfere with the theory, for the water may have been intermittent in its flow. The rock is very porous, and on being ground to a thin section is shown to be concretionary in structure. An analysis of the water of the spring (loc. cit.) showed that it contained over 1120 grains of mineral matter per gallon, of which 775 grains were sodium chloride and 206 grains sodium sulphate, with 66 grains of magnesium sulphate, 41 grains of magnesium carbonate, and 31 grains of calcium carbonate. An analysis by the author shows that there are 0.874 grains of silica. Samples of the rock composing the mound, and of the adjoining bluff were secured, and comparative analyses made, with the following results: GREAT COUNTRY SPIRIT ROCK. MOUND. Silica and insoluble residue 2.14 4.10 Oxides of Iron and Alumina 3.22 [5]2.66 Sulphuric Anhydride .00 0.34 Carbon Dioxide 40.90 39.10 Calcium Oxide 51.90 49.28 Magnesium Oxide 0.63 1.15 Water and organic matter, undetermined 1.21 [6]3.37 —————— —————— 100.00 100.00 Specific gravity 2.52 2.79