374 r. E. CLEMENTS SIGXIFICAXCE OF PALEO-ECOLOGY 



provides au assured method for the reciprocal correlation of climatic 

 changes and biotic movements in the past. These are involved in still 

 greater successional movements having to do with the appearance of new 

 biomes and the disappearance of preceding ones. The grand succession of 

 the globe falls readily into four great successions characteristic of the four 

 eras. In each era occurred major successional shifts which consisted, in 

 turn, of coseres and seres, such as are capable of actual stud}' today. 



The Attack ox developmental CorpxElatiox 



In planning an attack on the developmental correlation of plant and 

 animal communities in the past as well as in the present, the badlands 

 of the West early suggested the most promising field. A badland is an 

 extremely dynamic area, scarcely excelled by dunes in this respect. It is 

 one in which the rapid changes in habitat are clearly reflected in the de- 

 velopment of the biotic community. In addition they afford a unique 

 chance to relate minor cycles of erosion to climatic cycles and to fix the 

 dates of these CA'cles by means of the annual rings of the characteristic 

 shrubs. As is well known, the badlands are not only classic ground for 

 the paleontologist, but they also furnish a practically complete series 

 from the Permian through the Miocene. This series embraces practically 

 the whole panorama of terrestrial life and affords an exceptional oppor- 

 tunity for organizing the vast field of paleo-ecology. The recognition of 

 these facts has led during the past four years to an intensive study of 

 twenty or more badland formations in seventy-five localities in twelve 

 States. All the major areas have been visited, many of them several 

 times, and most of the minor ones as well. The most generous assistance 

 has been accorded by paleontologists, and the results will appear as soon 

 as the live-stock crisis in the West permits the transfer of interest from 

 the pressing ecological problems of the present to those of the past. 



SUMMAEY 



To sum up, paleo-ecology is characterized by its great perspective, due 

 chiefly to the absence of a large body of facts. This causes the funda- 

 mental correlations between the physical world and vegetation on the one 

 hand and between vegetation and the animal world on the other to stand 

 out in clear relief. As a consequence, paleo-ecology is an unspecialized 

 field in which the interrelations of climate, topography, vegetation, and 

 animals play the paramount role. The emphasis necessarily falls on 

 vegetation, because it is an effect of climate and topography, and a cause 

 in relation to the animal world, and hence serves as the keystone in the 

 whole arch of cause and effect. 



