8 THE POPULAR SCIENCE MONTHLY. 



of the Tertiary ages, except on mountains higher than any the conti- 

 nent now bears. In the Tertiary the climate was 6ub-tropical over all 

 the area of the United States soutli of the British line, as is shown by 

 the fact that palms and cinnamon-trees grew as far north as Van- 

 couver's Island and the falls of the Missouri. 



The relations which the great Quaternary lakes, Bonneville, La 

 Hontan, etc., bore to the former glaciation of the adjacent mountains 

 is an interesting Bubject of inquiry. As I have mentioned, it has been 

 suggested that it is the relation of cause and effect, but this is support- 

 ed by no proof, and opposed by strong circumstantial evidence. The 

 lakes and the glaciers may have been synchronous, and, to some extent, 

 co-operative phenomena ; but the relationship was rather fraternal than 

 filial, as they had probably a common parentage. 



The cause of the former wide spread of water-6urfaces in the un- 

 drained portions of the Gi-eat Basin was either more copious precipita- 

 tion or less rapid evaporation than at present. It is well known that 

 the supply of moisture of this region is derived from the rain-bearing 

 winds which blow steadily on to the land from the Pacific, and " the 

 testimony of the rocks" is conclusive to the effect that there has been 

 no change in the outline or elevation of the land, or the relations of 

 land to sea since the Tertiary age, which could have materially in- 

 creased or diminished the precipitation. 



So in regard to the topography of the interior. Since the end of 

 the Tertiary it has remained essentially the same. The hydrographical 

 basins have been filled and emptied, but the old beach-lines which mark 

 their sides prove that the country has remained substantially undis- 

 turbed. It is apparent, therefore, that the causes of any variation in 

 the amount of precipitated or accumulated moisture must be climatic 

 and not topographical. King, Gilbert, and Russell have shown that 

 there have been several alternations of wet and dry climate in the 

 Great Basin, and they are substantially in agreement that there have 

 been two wet and two dry periods, of which the last is the present. 



It would seem easy to determine by observation the relationship be- 

 tween the lakes and glaciers of that region, since some of the glaciers 

 descended far below the highest water-level, as was the case with the 

 Little Cottonwood glacier, to which reference has already been made, 

 but the actual contact of the glaciated surface and the lake sediments 

 is there covered and concealed by modern debris. The observations 

 made elsewhere by Gilbert and Russell will, when published, probably 

 demonstrate that which can now only be conjectured. We can con- 

 fidently predict, however, that it will be found that the same climatic 

 condition which produced the accumulation of water in the lake-basins 

 also caused the accumulation of congealed water on the highlands. A 

 greatly increased rainfall might produce lakes without forming gla- 

 ciers, but we appeal in vain to the facts or the imagination for a prob- 

 able cause of an increased oceanic evaporation, with a more abundant 



