PAST CLIMATES. 313 



results are those of Abbot and Fowle (1913), Douglass (1909, 1914), Hum- 

 phreys (1913), and Huntington (1907-1910, 1914). This is primarily because 

 they have concentrated their efforts upon the connection between the climate 

 of the present and of the immediate past, and because of the constant and skill- 

 ful use of a wide range of collateral evidence in its proper sequence. 



As a consequence, the natural sciences have for the first time reached the 

 stage where basic and thoroughgoing unification is possible. The acceptance 

 of the law of uniformity in climatology places the study of the atmosphere 

 in harmony with that of the geosphere proper, and makes it possible to inves- 

 tigate their interactions as unit processes. Between the geosphere and atmos- 

 phere hes the biosphere, acted upon by each and in its turn reacting upon 

 them. As already indicated, it is the endeavor of the present treatise to 

 harmonize the vegetation of the past with that of to-day, and to unify the 

 interactions of geosphere, atmosphere, and biosphere, in so far as the latter 

 consists of plants at least. It has already been affirmed that the vegetation 

 is the controlling part of the biosphere, and it is felt that the student of the 

 development and structure of animal communities must follow much of the 

 path already blazed by the plant ecologist, as well as extend it far beyond 

 the botanical boundaries. Hence, a basic and complete study of life is no 

 more possible without the aid of geology and climatology than it is possible 

 for these to have real point and meaning without the study of life. Thus, 

 while the analysis of nature into the various speciahzed natural sciences has 

 brought with it many advantages, the greater returns now seem to lie in the 

 direction of synthesis. At the present, we have come to realize that the study 

 of life must be made in its setting, i. e., in the environment of geologica;l, or 

 edaphic, and climatic factors which control it. This is ecology, the science 

 of the oikos or environment of the bio-community. When this inquiry is 

 extended into the past, it deals with the same things and differs only in its 

 time relation. Hence, the term paleo-ecology may well be broadened to 

 include the whole study of the interactions of geosphere, atmosphere, and 

 biosphere in the past. 



Evidence of past climates and changes. — ^Direct evidences of past climates 

 are found in the records of their effects. Inferential evidences are foimd in 

 the records of causes, such as deformation, gradation and vulcanism. The 

 latter will be considered under causes of climatic changes, while the direct 

 evidences drawn from recorded effects will be discussed here. These evidences 

 may be arranged in three groups: (1) geologic, (2) botanic, and (3) zooic. 

 Fossils are properly biotic, though there are also true geologic fossils, such as 

 fossil beaches, terraces, moraines, erosion foims, lava-flows, etc., if not indeed 

 all clastic strata also. The geologic evidences consist chiefly of (1) glacial 

 action, (2) terraces, (3) salt and gypsum beds, and (4) red beds. The plant 

 effects are recorded in (1) strates, (2) stases, (3) the rings of woody plants, both 

 present and fossil. The zooic evidence hes chiefly in animal fossils, but for 

 the human period in the culture relicts of man also. 



Geologic evidence. — ^The most striking chain of geologic evidence is that 

 which has led from the polar and alpine glaciers of the present back through the 

 Pleistocene glacial period to the more remote glacial periods of Paleozoic and 

 earlier times. If the principle of uniformity in the action of forces in the 

 present and past be once accepted, this chain of glacial evidence seems to have 



