CLIMATE AND TERRESTRIAL DEPOSITS 277 



been seen by the writer or described by others and no carbon from the 

 plant tissues is ever preserved. Tliese characteristics are opposed 

 throughout to those of the overlying carbonaceous beds of the true 

 Carboniferous. In these the carbon is preserved, impressions of logs 

 are abundant, the vegetation is coarse and luxuriant, and grasslike 

 forms give place to a water-loving forest growth. The roots preserved 

 in the underclay show no such tendency to penetrate constantly down- 

 ward and in the case of the stigmaria are developed into stolen-like 

 forms such as are possessed by many existing marsh plants. 



The conclusions as to climate, based on the character of the vegeta- 

 tion in the case of these late Paleozoic formations and determined from 

 adaptive relations observed to exist at present in quite different divi- 

 sions of the vegetable kingdom, are thus seen to be in harmony with 

 conclusions based on a number of other and independent lines of 

 evidence. The latter, however, cannot be given at this place. 



The animal life also shows adaptations to the climate, but these 

 are far from being as strongly marked or so dominated by climate 

 as in the case of plants, so that neither can a discussion of such general 

 characteristics be considered under the present subject. 



EFFECTS OF ARID CLIMATES UPON FLUVIAL AND PLUVIAL 

 DEPOSITS 



Chemical characteristics, evaporation deposits. — Arid climates, 

 those of true deserts, typically possess no drainage to the sea and 

 no agriculture is possible without either natural or artificial irrigation. 

 Fluvial and pluvial deposits may, however, be abundantly developed, 

 owing to the torrential nature of the occasional lains acting upon a 

 loose and unprotected mantle rock. In this hasty transfer of dis- 

 integrated rather than decayed rock debris but little leaching is hkely 

 to occur, soluble and insoluble materials remaining together, the 

 two tending to become somewhat separated by later and local action. 

 The rainfall of such regions is, in the temperate zone, less than ten 

 inches per year. 



As noteworthy examples of deltas in arid climates may be cited 

 those of the Volga, the Indus, the Nile, and the Colorado. The lime 

 in such may form still more striking inorganic deposits than the " Kan- 

 kar" of the subarid flood plains of India, forming such incrustations 



