INDEX. 



395 



Niagara gorge, 56; breaks and 

 revolutions, 45. 



Time estimates, data of, 56; geolog- 

 ical, 57; by geological deposits, 

 57; hypothetical, 49; Kelvin, 56; 

 tidal friction, 56, uncertainties in, 

 49; Ward, 48. 



Time-periods and terranes, 28. 



Time-ratios of Dana, 47, 54, 61 ; Wal- 

 cott, 61; Williams, 6l. 



Time since glacial age, 57. 



Times, geological, 26; relative 

 lengths of, 54. 



Time-scale, and fossils, 66; standard 

 units of, 31. 



Time-values of characters and rank, 



93- 



Thales and Anaximander, 152. 

 Theca, 91. 



Thecacea, evolution of, 256, 262. 

 Thickness of deposits, 60; of rocks, 



57. 58. 



Transition formation, 13, 19. 

 Transmitted characters, 192. 

 Transmission and acquirement of 



variation, 158. 

 Transmutation theory of lonians, 



152. 



Trullacea, evolution of, 256, 262. 

 Tunicata, definition of, 204; de- 

 scribed, 244. 

 Turbinolidce, rate of differentiation, 



85. 



Two scales, necessity of, 66. 

 Typical specific characters, 115. 

 Types of Spirifer, in continuous 



series, 313; at initial period, 314. 

 Typical structure and types, 236. 



Uebergangs Gebirge, 13, 16. 



Unconformity and revolution, 40. 



Undifferentiated cell, 221. 



United States Survey nomenclature, 

 30. 



Units of chronology, 51 ; of the time- 

 scale. 77. 



Unstratified rocks, 18. 



Use and disuse, in origin of species, 

 195- 



Values of units of time-scale, 64. 



Variability of Atrypa, Hall, 317; in 

 Darwin's theory, 193; an inherent 

 characteristic, 184; and perm- 

 anency of characters, 311. 



Variation, acquirement of, 158; dis- 

 continuity of, 199; and evolution, 

 158; and mutability assumed in 

 discussion of origin of species, 

 183; in thickness, 58; the unsolved 

 problems of, 198. 



Variations of Atrypa reticularis^ib; 

 and mutations, 70. 



Varietal characters, 115; alone ad- 

 justed, 143. 



Varieties, 207; in Darwin's theory, 

 194. 



Varying antiquity of characters of 

 Spirifer logani, 190; conditions and 

 strata, 73. 



Vermes, definition of, 204. 



Vertebrata, definition of, 204. 



Volutions of spires in Helicopeg- 

 mata, 286. 



Von Baer's classification, 234. 



Wallace, Alfred R., and distribution, 

 112; on species, 298. 



Walther, Bionomy, 116; conditions 

 of environment, 116. 



Ward, time estimate, 48. 



Water, as environment, 113. 



Water-vascular system, 229. 



Wernerian theory of formations, 16. 



Werner and the Lehmann classi- 

 fication, 13; and mineral char- 

 acters, 17; classification of rocks, 

 17, 19. 



What are species? 149; is evolved ? 

 265, 269; is evolved, summary, 

 272. 



Zittel's classification of Mollusca, 

 239; on fossils, 82; translation 

 from, 135, 329 343. 



Zoantheria, 84; of each era, 84; and 

 the time-scale, 85. 



Zonal adaptation, of Gastropoda, 

 140; distribution of Ctenobran- 

 china, 136. 



Zonaric plankton, 116. 



Zone, 69, 113. 



Zones of Ammonites, 28; of environ- 

 ment, of Gastropods, 132; and 

 hemera, 68; of ocean, Forbes, 117; 

 Verrill and Smith, 117. 



Zoological and geological biology, 

 98; specimen like a fossil, 163. 



Zoologist, method of, 5. 



Zygospira, jugum in, 284. 



