X CONTENTS. 



system — The Post-paleozoic or Appalachian revolution, 34. — Triassic 

 system, 35. — Jurassic system — Cretaceous system, 36. — Tertiary sys- 

 tem — Quaternary system — Fossils the means by which the age of a 

 system is determined, 37. 



CHAPTER III. 



THE DIVISIONS OF THE GEOLOGICAL TIME-SCALE AND THEIR TIME- 

 VALUES. 



The systems and geological revolutions — Geological revolutions local, not 

 universal, 39. — Revolutions expressed by unconformity and disturb- 

 ance of strata — Appalachian revolution, 40. — Taconic revolution, 41. — 

 Acadian revolution — Appalachian revolution — Palisade revolution, 42. 

 — Rocky Mountain revolution, 43. — The division line between the Cre- 

 taceous and the Tertiary — Columbia River lava outflow, 44. — Glacial 

 revolution — Erosion of river canons as gauges of time duration — Con- 

 tinental value of revolutions as time-breaks in the history of North. 

 America, 45. — Time-scale and the geological revolutions of the Amer- 

 ican continent — Revolutions made interruptions in the record, 46. — 

 Time-ratios, or relative time-value of the several systems, 47. — Ward's 

 estimate, 48. — Corrections and elements of uncertainty in these esti- 

 mates — Estimates of actual length of time highly hypothetical, 49. — 

 Systems the standard units of geological chronology — Geologic Eras 

 and Times and their names — Division of the Eras into Periods, 51. — 

 Period a recognized division of an era — Standard Periods and their 

 names, 52. — Use of the term Epoch in the time-scale — A comparative 

 time-scale for the study of the history of organisms, 53. — Importance 

 of a standard time-scale, 54.— Actual length of geological time, 55. — 

 Data upon which time-estimates are made — Phj-sical and astronomical, 

 56. — Geological — Method of computing time from thickness of rocks, 

 57. — Errors arising from estimated values in the computations, 58. — 

 Errors affecting the values of actual, not relative, time-lengths — Vari- 

 ous estimates of the length of geological time, 61. — Average of the 

 estimates of only hypothetical value — Provisional units of the time- 

 scale assumed to be of equal value, 63. 



CHAPTER IV. 



STRATIFIED ROCKS— THEIR NATURE, NOMENCLATURE, AND FOSSIL 



CONTENTS. 



Common usage in classifying stratified rocks — Fossils of higher value than 

 strata for determining time-relations, 65. — The necessity of two scales ;. 

 strata furnishing the data for the formation-scale, and fossils forming- 

 the basis of the time-scale — Use of the terms Period and Formation, 

 66. — Strata parts- of a geological formation ; fossils the marks of a 

 geological period, 67.— The Hemera of Buckman — The terms Age of 

 Reptiles, Planorbis Zone, etc., 68. — Nomenclature of the International 

 Congress of Geologists — Fauna and flora — Horizon — Zone and stratum 

 — Facies, 69. — Area, province, region — Geological range and geo- 

 graphical distribution — Variations and mutations — Development and 

 evolution — Initiation and origin, 70. — System — Geographical condifions- 

 determining the local character of stratified rocks, 71. — Varying condi- 



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