298 



MAN AND THE GLACIAL PERIOD. 



quicksand occurred to a depth of three hundred and 

 twenty feet, where there appeared indications of a former 

 surface soil lying just above the bed-rock, from which 

 the clay image was brought up in the sand-pump. 



Fig. 96. — Three views of Nampa image drawn to scale. The middle one is from 

 a photograph. 



I devoted the summer of 1890 to a careful study of 

 the lava deposits both in Idaho and in California, with a 

 view to learning their significance with reference to these 

 discoveries. The main facts brought to light by this 

 investigation are that in the Snake River Valley, Idaho, 

 there are not far from twelve thousand square miles of 

 territory covered witli a continuous stratum of basaltic 

 lava, extending nearly across the entire diameter of the 

 State from east to west. Nampa, where the miniature 

 image was discovered, is within five miles of the western 

 limit of this lava-flow, and where it had greatly thinned 

 out. The relative age of the lava is shown by its relation 

 to Tertiary beds of shale and sandstone, containing numer- 

 ous fossils of late Pliocene species. These are overlaid in 

 this vicinity by the lava, thus determining its post-Ter- 

 tiary character. Examination with reference to the more 

 precise determination of age reveals channels of erosion 

 formed since the lava-flow took place, which, when studied 

 sufficiently, will probably lead to valuable approximate 



