ii2 Introduction to Life of the Lakes. 



result is striking", for we have the exact cast 

 of the inner cavity of a bivalve, its lower half 

 a dark opaque sea mud, its upper half a fine 

 translucent chalcedony of rich carnelian tint. 

 Or if we take the same process as it may 

 be traced in a different fossil, we have here 

 the jaw of a rhinoceros. We have the com- 

 pleted result in this fossil, and the entire pro- 

 cess is this: The jaw with its teeth in place is 

 washed into the deep waters of an Eastern 

 Oregon lake; it sinks into the soft mud of the 

 lake bottom. In time the mud is pressed into 

 every accessible crevice of the bone and its 

 dental contents, but in the teeth that are 

 entire there remains a whole set of cavities 

 inaccessible to this lake mud. It is into these 

 nerve cavities that the liquid silica is forced 

 and in which it is preserved; and if we recall 

 the sea shell with its quartz infiltration, this 

 result often obtains: That if the shell is so en- 

 tirely closed as to wholly exclude the muddy 

 sediment, then the whole inner cavity is lined 

 with silica, clear as crystal, or if almost filled 

 with quartz, as often happens, then a small 



