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 Physical 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 

 Fades, 69. Area, province, region Geological range and geo- 

 graphical distribution Variations and mutations Development and 

 evolution Initiation and origin, 70. System Geographical conditions 

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



