206 



INDEX 



Sedimentary rocks, distribution of, 61 

 rocks, origin of, 57 

 rocks, thicknesses of, 61, 67, 68 

 Seeds, 97 



Selection, natural, 106 

 Sharks, 120 

 Sheep, 177, 178 

 Shellfish, 90 

 Shelter, dependence of, on climate, 154 



effect of, on energy, 156 

 Silica, 100 



Silurian period, 46, 76, 79, 111, 122, 123 

 period, climate of, 55 

 period, diastrophism in, 122, 144 

 period. North America in, 72 

 Sloths, fossil, 74 

 Snails, 90 

 Snow, 54 

 Socrates, 151 

 Soil, 155 

 Solar energy, 102 



energy, rhythms in, 109 

 prominences, 16 

 system, elements of, 5 

 system, Kant's hypothesis of evolu- 

 tion of, 10 

 system, Laplace's theory of origin of, 



10 

 system, plantesimal hypothesis of 

 origin of, 13 

 Sollas, W. J., 60 

 Space, interstellar, transportation of 



life through, 96 

 Spallanzani, L., 92 

 Speech, invention of, 174 

 Spencer, H., 86 

 Sponges, 113, 114 

 Spontaneous generation, 90, 91 

 Spores, 96, 97, 98 

 Squids, 73, 114, 115 

 Star streams, 7 

 Stars, 6, 13, 15, 23 

 chances of close approach among, 22 



Stars, mode of tidal disruption in, 15 



new, 9 



Wolf-Rayet, 9 

 Static forms, 81 

 Stegocephalia, 125, 145 

 Stegosauria, 130, 132 



characteristics of, 131 

 Stegosaurus, 130 



Stellar system, sun a member of, 6 

 Stockholm, optimum temperature in, 



as shown by death-rate, 167, 169 

 Storms, changes in track of, 187 



effect of, on human energy, 166 



present belt of, 187 

 Strand-line, 76, 120 

 Stratification, density, 36 

 Struggle for existence, 73, 81 

 Suess, E., 38 

 Sulphur, 102 

 Sumatra, 188 

 Sun, 4, 10, 12, 13, 19, 20, 44, 98, 105 



ancestral, tidal disruption of, 16 



as life factor, 54 



as member of stellar system, 6 



critical velocity of, 17 



origin of, 46 



prominences shot out from, 16 



rotation of, 20 

 Sunshine, 102 



Surface processes, in earth, 43 

 Swan, 89 



Sweden, iron in, 155 

 Swim-bladder, 120 

 Swine, 136 



Tapirs, 136 

 Tartrates, 107 



Temperature, changes in, effect of, 

 165, 172 



effect of, on death-rate, 163, 164, 165 



optimum, 167 

 Terrestrial foot, evolution of, 123 



foot, origin of. 111 



types, influence of aridity on, 127 



