8o The Shoshone Island. 



than nine hundred feet. Through all of these 

 the DesChutes had worn its channel without 

 reaching- the bottom of this underlying hard 

 basalt. 



Manifestly the upper and newer portions 

 of the hill were built of lighter materials, 

 mixed more and more, as one ascended, with 

 layers of volcanic ashes, and where the layers 

 were of denser materials, showing weathering 

 and erosion between the eruptions to which 

 they were due, at once suggesting that these 

 eruptions were separated by considerable in- 

 tervals of time. 



In marked contrast with this condition of 

 these upper layers seemed that of the denser 

 ones of the lower division, indicating rapid 

 successions of outflows with no time for 

 weathering between them. The enormous 

 eruptive activity indicated by these lower de- 

 posits must have occurred in early Tertiary 

 times and in sight of our Shoshone island. 



While these denser layers of basalt were 

 poured out over the surface in earlier stages of 

 this great eruption, another feature marked 



