Radioactive treatment, physical basis of, 251. Radioactivity and heat emission from average igneous rock, 126; rarity of, established by haloes, 241, 243. Radium, chemical nature and transmutation of, 244-245; emanation of, 245; rays from, 253, 254; table of family of, 253; period of, 253; small therapeutic value of, 254. Radium C, therapeutic value of, 254; rays from. 254; generation of, 254. Rationality, conditions for development of, 163. Rays, similarity in nature of gamma, X, and light rays, 248; effects on living cell, 251; penetration of, 251. Reade, T. Mellard, finding age of ocean by calcium sulphate, 13. Recumbent folds, formation of, 155 _et seq._ Regelation, 284; affecting glacier motion, 285. Reversal, photographic, explanation of, 211. Richards and Lembert, atomic weight of lead, 27. Richter, Jean Paul, Dream of the Universe, 200. Rock salt in the ocean, amount of, 13. Rocks, average composition of, 43; radioactive heat from, 126; rate of solution of, 36. Russell, I. C., river supply of sediments, 10. Rutherford, Sir E., determination of age of minerals, 19, 20; age of rocks by haloes, 22; derivation of actinium, 226; artificial halo, 229; number of alpha rays from one gram of radium, 237. S. Salt range deposits of India, 134. 135. Saltness of the ocean due to denudation, 41-46. Salisbury (and Chamberlin), the Larimide range, 121. Salmon, Rev. George, on creation, 301. Satellite, velocity of, in its orbit, 191; method of finding path of, over a rotating primary, 189 _et seq._; direct and retrograde, 178; ultimate end of, 178; path of, when falling into primary, 179; effect of Mars' atmosphere on infalling satellite, 179; stability of close to primary, 180; effects of, on crust of primary, 180 _et seq._ Schiaparelli, observations on Mars, 165 166. Schmidt, C., original depth of Alpine layer, 131-148; structure of the Alps, 152. Schmidt, G. C., on photo-electricity, 207, 208; effect of solution on photo-electric activity, 213. Schuchert, C., average area of N. America during geological time, 16. Sedimentary rocks, average composition of, 43; mass of, determined by sodium index, 47. Sedimentation a convection of energy, 133. Sediments, average river supply of, 11; on ocean floor, mass of, 48; average thickness of, 49; precipitation of, by dissolved salts, 56-58; radioactivity of 130; radioactive heat of, influential in mountain building, 130, 131; rate of collecting, 7; determination of mass of, 8; river supply of, 10; total thickness of, 6. Semper, energy absorption of vegetable and animal systems, 78. Sensitisers, effects of low temperature on, 210. Simplon, radioactive temperature in rocks of, before denudation, 132. Skates, early forms of, 273; principles of construction of, 273 _et seq._; action of, on ice, 276; bite of, 278-280. Skating not dependent on smoothness of ice, 260; history of, 273. Skating only possible on very few substances, 279. Soddy, F., on isotopes, 24.