STUDIES OF SPECIAL LACUSTKAL HISTORY. 107 



Great Basin, while Lake Laliontan flooded a series of irregular valleys on 

 the west side of the same great area of interior drainage and is now re[)re- 

 sented by Pyramid, Winnemucca, Walker, Carson, and Iluniholdt lakes, 

 Nevada, and by Honey lake, California. 



These two ancient lakes were contemporaries, and, although differing 

 in their histories, bear similar testimony in reference to climatic changes 

 and supplement each other's records in a remarkable manner. Their 

 hydrographic basins joined each other in north-eastern Ne\ada, for a 

 distance of about twenty-live miles, and together occu[)ied the entire 

 width of the Great Basin. Lake Bonneville received its water supply 

 from the Wasatch and Uinta mountains, then snow-clad throughout the 

 year and holding glaciers of the Alpine type in many of their valleys. 

 Several of the ice streams on the precipitous western slope of the Wasatch 

 mountains reached nearl}- to the ancient lake Avhich washed the base of 

 the range, and one of them was prolonged for a short distance into its 

 waters. Lake Lahontan derived its principal water supply from the Sierra 

 Nevada, which formed the western rim of its drainage basin for a distance 

 of 250 miles, and, like the eastern borders of the Bonneville basin, was 

 glacier-covered. 



Lake Bonneville at the time of its maximum extension had an area of 

 19,750 square miles, and a hydrographic basin 52,000 square miles in 

 area. The more irregular water surface of Lake Lahontan was 8,422 

 square miles in area, and occupied the lowest depressions in a hydro- 

 graphic basin containing 40,775 square miles. The great size of the 

 hydrographic basins of these lakes in comparison Avith their extent of 

 water surface, is a noteworthy feature. The I'atio of the extent of lake 

 surface to area of hydrographic basin in the case of Lake Bonneville was 

 as 1 to 2.6, and in the case of Lake Lahontan about 1 to 5. The corre- 

 sponding ratios in the basin of Lake Superior are as 1 to 1.72 ; and for 

 the combined Laurentian lakes as 1 to 3.19. The small extent of the 

 ancient lakes of the Great Basin in comparison with the areas draining to 

 them, more especially in the case of Lake Lahontan, indicates that the 

 climate of their time was not markedly humid. 



The maximum depth of I^ake Bonneville as recorded by beach lines 

 on the mountain forming its shores, and on the precipitous islands now 

 rising in Great Salt lake, was 1050 feet. The greatest depth of Lake 

 Lahontan was 886 feet. 



The most striking difference in connection with these two ancient 

 seas is in reference to overflow. Tlio waters of Lake Bonneville rose 



