474 



INDEX 



Sea level, 254. 



Sea life, Permian, 392. 



Sea urchins, 297, 423. 



Seals, 462. 



Seas, Mississippian, 371. 



Secondary rocks, 41. 



Secretions, 122. 



Sedimentary rock, 19, 37, 40. 



structure, 54. 

 Sedimentation,Mississippian,370. 



Ordovician, 340. 

 Sediments, formation of, 37. 

 Seed ferns, 293. 

 Seed plants, 294. 

 Seepage, 110. 

 Shale, 39. 

 Shark, 367, 374. 

 Shelves, continental, 256. 

 Shore current, 246. 

 Shore lines, 238, 250. 

 Shores, ocean, 237. 

 Silicates, 20. 

 Sills, 50. 



Silurian period, 349. 

 Silver, 120. 

 Sinks, 118. 

 Siphuncle, 299. 

 Slate, 43, 82. 



fossiliferous, 44. 

 Slickensides, 71. 

 Slump, 115. 

 Snail group, 298. 

 Snow line, 191. 

 Snow field, formation of, 191. 

 Soils, 16. 

 Solution by ground water, 116. 



zone of greatest, 117. 

 Source of ground water, 107. 

 Spermatophytes, 294, 416. 

 Spit, 247. 

 Sponges, 295. 

 Spores, 293. 

 Springs, 110. 



calcareous, 111. 



deep-seated, 113. 



ferruginous, 111. 



hillside, 111. 



medicinal, 110. 



Stack, 244. 

 Stalactites, 120. 

 Stalagmites, 120. 

 Starfish, 297. 

 Stock, 51. 

 Stoss slope, 219. 

 Strata, competent, 67. 



folded, 67. 



incompetent, 67. 

 Stratification, 37, 54. 



in a sand dune, 93. 

 Stratified rocks, 19. 

 Stratum, 54. 

 Stream, beheaded, 169. 



degrading, 134. 



graded, 135. 



intermittent, 139. 

 Stream piracy, 169. 

 Streams, work of, 125. 

 Striate, 217. 

 Strike, 69. 



Structural valleys, 138. 

 Structure, columnar, 53. 



massive, 52. 

 Structures of sedimentary rocks, 



54. 



Submergence, Champlain, 463. 

 Subsequent falls, 159.J 

 Subsoil, 16. 

 Sun cracks, 56. 

 Suture, 299. 

 Syenite, 29, 30. 

 Synclines, 66. 

 System, mountain, 275. 



Taconic revolution, 348. 

 Talus, 90, 102. 

 Teleosts, 416. 

 Temperature, 100. 



critical, 81. 

 Tepee buttes, 432. 

 Terrace, 188. 



alluvial, 183. 



river, 152. 



wave-built, 241. 



wave-cut, 241. 

 Terrigenous deposits, 256. 

 Tertiary climate, 437. 



