290 PAST CLIMATES AND CLIMAXES. 



gymneosere and angeosere respectively. The eosere of the Eophytic period 

 must have been extremely brief in terms of life-forms, consisting indeed of but 

 variations of the algal and bryophyte forms. Hence, while the Eophytic era 

 must be taken into accoimt theoretically, actually its features can be traced 

 only in the faintest outline. Whenever it is desired to emphasize the time 

 relations of the successive eoseres, the names proposed above may well be 

 replaced by those based upon the eras instead of upon the dominant floras, 

 namely, paleosere, meseosere, and ceneosere. Each of these is a major succes- 

 sional unit, consisting of seres, cUseres, and eoseres, while taken together they 

 constitute the geosere. 



THE PLANT RECORD. 



Nature. — From the manner in which sedimentary deposits are laid down, 

 the plant fossils in them fvu-nish conclusive evidence of the major facts in 

 succession. The successive strata are usually decisive as to the sequence of 

 plant populations, exceptions occurring only where fossils have been removed 

 and redeposited, or where great unconformity occurs. Even where the local 

 record is consequently misleading or interrupted, the general record is readily 

 established by the comparison of contemporaneous strata in various localities. 

 But, while the record of the general sequence of populations is fairly adequate, 

 only an infinitesimal number of the details of structure and development have 

 been preserved. Nevertheless, since the climax vegetations of the past 

 covered such vast areas, and since the development of seres and the production 

 of zones must have occurred constantly throughout the vast stretch of time 

 represented by an eosere, it is possible to reconstruct the development in 

 much detail. 



The fossil record furnishes both direct and indirect evidence of the course 

 of succession in the past. By far the greatest mass of evidence is indirect. 

 Fossilization usually did not occur on the spot actually occupied by a plant com- 

 munity. In the usual procedure, plants or plant parts, especially leaves, must 

 have been blown or washed into the water, or may have merely fallen into the 

 water in the case of riparian communities. In all such fossil horizons, direct 

 evidence as to the structure or development of the adjacent communities is 

 wanting. The sequence of stages and of zones can be ascertained only through 

 patient reconstruction by the method of succession. In short, the problem 

 is to retrace the development and structure of the cUmax formation from a 

 more or less imperfect knowledge of the characteristic flora. Moreover, this 

 knowledge is necessarily much more complete for the climax units than for 

 the developmental ones, since climax areas are vastly more extensive. 



Direct evidence of succession in the past is found only where communities 

 grew in water or wet places, with the result that the preservation of plants or 

 plant parts as they fell was so nearly complete as to give a fairly detailed 

 picture of the consocies as well as the climax. Fortunately, such plant 

 deposits occur in each vegetation era, though they are of less importance in the 

 Mesophytic. They are of course best represented in the coal measm-es of the 

 Paleophytic, in the lignitic deposits of the Cretaceous, and in the peat eoseres 

 of the Pleistocene and the present. From the standpoint of succession, the 

 peat horizons are much the most important, since they furnish an all but 

 infalhble guide to the changes of vegetation and climate from the Pliocene to 



