PALEIC INDICATORS. 103 



region, it is possible to reconstruct the biome in much detail and with the 

 greatest possible certainty. For example, the geologic evidences of arid 

 climates at different periods must be regarded as more or less tentative until 

 confirmed by plant or animal indicators of aridity. When both occur, as in 

 the Miocene, the chain of evidence is complete. It then becomes possible 

 with the aid of the indicator relations discussed here to present a fairly 

 detailed and complete picture of the structure and development of the biotic 

 climaxes of the past. The general features of this have already been done for 

 animftla by Osborn (1910), and much progress has been made in doing this for 

 the associated plants and animals of the Bad Land horizons of the West. 



Paleic indicators of climates and cycles. The evidences of past cUmates 

 and cUmatic changes have been summarized from the geologic, botanic, and 

 zooic aspects (Plant Succession, 313). Since plants are the most immediately 

 responsive to cUmatic influences and constitute the best indicators, they are 

 chiefly considered here. The grand climates of geologic time are indicated by 

 corresponding great floras and faunas, which have served as the basis for the 

 division into eras. During each of the latter, climatic differentiation in both 

 space and in time has been faithfully reflected in the vegetation, and the com- 

 bined effect of cUmate and vegetation in the fauna. It seems highly probable 

 that a considerable differentiation of climates and climaxes took place during 

 the Paleophytic era, and that this was increased during the Mesophytic era 

 to become the most outstanding feature of the biosphere during the Ceno- 

 phytic. Thus, while each era is indicated by a particular climax flora, it also 

 exhibits climax formations as indicators of more or less distinct climates, just 

 as is the case to-day. While the grand deformation cycles which produced 

 the eras were marked by a changed flora and fauna, the major deformation 

 cycles and grand sun-spot cycles are thought to correspond with shiftings of 

 cUmate and vegetation, such as are indicated for the Pleistocene. These have 

 to do with climaxes as indicators, and it seems a fair assumption that the 

 series of climaxes found in the Pleistocene shiftings likewise occurred in some 

 degree in the earUer cliseres of the Mesophytic and Paleophytic eras. The 

 constitution of the cUmaxes during the various eras and their relation to 

 climatic cycles is discussed in some detail in "Plant Succession" (356, 406, 

 419) and need not be repeated here. 



Paleic indicators of succession. Apart from the great successional move- 

 ments involved in the change of floras and the shifting of cUmaxes, there must 

 have been innumerable examples of seres and coseres in every era. Primary 

 areas of erosion and deposition were probably more abundant than to-day, 

 and primary succession must have been the rule, though secondary seres were 

 not unknown. Coseres resulting in the formation of coal or peat have occurred 

 repeatedly from the Paleophytic to modern times, while in periods of great 

 volcanic activity, such as the Miocene, they were produced by deposits of 

 volcanic dust. While each era possessed its particular flora, all the Ufe- 

 forms were represented. Thus, while the genera typical of the various serai 

 stages during the Paleophytic and Mesophytic are practically all different 

 from those of the Cenophytic and to-day, the vegetation-forms and habitat- 

 forms are the same or nearly so. With reference to the genera which con- 

 stituted the serai dominants and hence served as indicators of habitats and of 

 succession, the hfe-forms have been discussed in "Plant Succession" (pp. 354, 



