Analytical Abstracts of Current 

 Literature. 



The Relation Between Base leveling and Organic Evolution. By J. B. 

 Woodworth. (American Geologist, October, 1894, Vol. XIV., 

 No. 4, pp. 209-234.) 



In the historical sketch the writer speaks of the former strong belief of the 

 British geologists in marine action as the origin of baseleveling, due in large 

 measure to their insular position. They have recently been awakened by the 

 work of the continental geologists in regard to baseleveling by meteoric 

 agents. 



In America, Powell, Gilbert, Davis, McGee, and others have established a 

 cycle of existence for rivers and their valleys, ranging from youth, in a newly 

 elevated country, through adolescence, maturity, and so on into old age, when, 

 the land remaining stable, a peneplain will be formed. An uplift will revive 

 the streams and start a new cycle. Many other points of interest are 

 brought out by these writers in regard to the history of river systems. 



Under the general effect of river changes on fluvial faunas, the important 

 relation of the topographic history to the distribution of fresh-water fish and 

 mollusks is shown. This may be through (1) head-water division, (2) ante- 

 cedent streams, (3) alluviation, (4) slight submergence, (5) elevation and 

 revival of streams. 



Effect of baseleveling of a mountainous region is discussed, including the 

 fading away of divides, the degradation of uplands, spread of lowland con- 

 ditions, the peneplain as an open field for land life, uplift and dissection of 

 the peneplain. The Jura-Cretaceous peneplain is discussed at length, both 

 in its topography and its influence on life. It forms a conspicuous topographic 

 feature in eastern North America, and traces of it occur on the Pacific coast. 

 It is well developed in New England, Middle Atlantic states, and southward. 

 At the close of the Cretaceous the peneplain was elevated when streams began 

 to cut valleys, and another Tertiary baselevel had ;almost been completed 

 when a new uplift caused rejuvenation. 



The influence of the peneplain on life is most pronounced, being most 

 favoi able for reptiles, which abound in such great numbers. Reptiles are 

 characteristic lowland forms. They can endure the cold of high altitudes or 

 latitudes only by falling into a torpor. The conditions being so favorable, 

 they thrive in such vast numbers and are of such great size that the mammals 

 are virtually driven to the uplands and almost extinguished. Several theories 



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