34 PROCEEDINGS OF THE AXX ARBOR MEETING 



and the measurements of geologic time/"' pages 753-809, where it is con- 

 vincingly shown tliat because of tectonic movements in late Tertiary and 

 Pleistocene time and the consequent high stand and great relief of the 

 continents, the rate of erosion, and correlatively the rate of sedimenta- 

 tion, far exceeds the average rate of erosion and sedimentation of earlier 

 geologic time, "ten or fifteen times the rate for all of geologic time since 

 the opening of the Paleozoic." 



Under the caption "Rate of sedimentation determined by subsi- 

 dence/' ^^ Barrell emphasizes a geologic relation that deserves noting. 

 In connection with the recognition of the control of baselevel over botli 

 erosion and deposition, it is stated that "on the surface of deltas or the 

 floors of epeiric seas sedimentation records the rate of subsidence, not 

 the rate nor the amount of denudation." The sul)sidence in general is 

 not due to the load of sediments. "It may readily be granted that this 

 load of sediment, acting in the same direction as the forces initiating 

 subsidence, would tend to continue it and carry it to greater depths ; but 

 without the sediments, deep water would almost surely have resulted, 

 such as exists at ])resent in the southern part of the Gulf of California. 

 a geosyncline filled only at its northern end."' 



THE CLIMATIC FACTOR IN DEPOSTTIOX 



One of Barren's longest jDapers on problems oL' sedimentation is en- 

 titled "Relations between climate and terrestrial deposits. ^^ In the gen- 

 eral introduction to this series of articles he says : 



"The environment of the hinds may be chissified into three fundamental and 

 independent factors — tlie rehitions to tlie surrounding seas, the topography 

 wliicli forms tlieir surfaces, and tlie climates which envelop them — each of 

 major importance in controlling the character of the lands and the evolution 

 of their inhabitants. 



"The third great problem of terrestrial environment, the succession of ancient 

 climates, lags still farther behind in development, but is no less important in 

 a complete understanding of the history of the earth and its inhabitants. This 

 lack of development is doubtless due to the intangible nature of climate and 

 the absence of direct record of its geologic changes. When it is considered, 

 however, how fundamental are the relations of continental deposits to the 

 climates in which they are formed, it is seen that the record of geologic cli- 

 mates, while indirect and largely awaiting interpretation, is nevertheless in 

 existence. 



^^ Rhythms and the nioasnremeuts of geologic time. Bull. Geol. Soc. Am., vol. 2S. 

 1917, pp. 78.")-780. 



".Tour. Geol., vol. IG. VM)H, pp. l.".!>-ir»(), •J.3.")-i'<»,->. :>,(i:!-:;s4. 



