GEOLOGY. 



Antevs, Ernst, University of Stockholm, Sweden. On the Pleistocene history 

 of the Great Basin. 



In July and August 1922 the writer studied the deposits in the ancient lakes 

 Lahontan, Bonneville, and Mono, in the Great Basin, in order to get a better 

 knowledge of their Pleistocene history and to be able more accurately to 

 connect this with the history of the northern part of the continent. It was 

 hoped that the clays deposited in the lakes would show annual lamination, 

 eventually enabling direct correlation between the high-water stages in the 

 Great Basin and the disappearances of the ice sheets in the North, but the 

 sediments were found on the whole to lack seasonal banding. In the memoir 

 submitted to the Carnegie Institution of Washington the times of the lakes, 

 therefore, have been discussed from a broad climatological basis. An analysis 

 and review of the climatic conditions during glaciations and during the post- 

 glacial epoch have been given. The chief events in the Great Basin have been 

 found to have run parallel with the large events in the North. In the North 

 four or possibly five glacial epochs, separated by warm interglacial periods, 

 have followed each other. In the Great Basin, glaciations combined with 

 expansions of the waters have alternated with arid periods. The high-water 

 stages were due to heavier precipitation than at present and to little evapo- 

 ration because of low summer temperature. The relatively heavy rainfall was 

 connected with the changes of climate that checked the expansion of the ice 

 sheets and caused their shrinking. It was a consequence of decrease of 

 precipitation over the land ices, possibly caused by rise of temperature. The 

 mountain glaciations and the slightly lagging high stands of the lakes in the 

 Southwest were contemporaneous with the climaxes of the great glaciations 

 and the first time of ice retreat. The arid periods, some of which may 

 have been more pronounced than at present, corresponded to the interglacial 

 epochs. 



In the mountains in the Southwest records of three glacial epochs have been 

 recognized, and in the Lahontan Basin sedimentary records of three or 

 perhaps four, in the Bonneville Basin of two, and in the Mono Basin of two 

 or perhaps several high-water stages are known at present. Doubtless there 

 were in the Southwest as many glaciations and lake stages as there were gla- 

 cial epochs in the North, and the last ones corresponded to the last glacial 

 epoch — that is, they date some 30,000 years back. 



As the ice sheets disappeared an adjustment of climatic conditions took 

 place through which the belt of heavier rainfall again shifted northward. 

 Shore lines below the highest stand of the Pleistocene lakes and alternations of 

 beds of different coarseness indicate stationary lake-levels and small fluctua- 

 tions during the general fall of the waters. While the post-Lahontan freshen- 

 ing of Pyramid and Winnemucca Lakes, Nevada, may have occurred by over- 

 flow through the Emerson Pass, 70 feet above Pyramid Lake, into the Smoke 

 Creek Desert, Walker Lake, as lacking an adjacent evaporation pan, may have 

 been dry at a later date, or some thousand years ago. Correlation between 

 these fluctuations and the variations in width of the growth rings of the big 

 tree had better be postponed till the factors of the radial growth become more 

 satisfactorily known. 



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