Douglass: Vertkhrates krom Montana Tkrtiarv. 147 



There is much volcanic dust in the beds, some strata being 

 made u|) almost entirely ot" this material. Of course these beds of 

 pure dust must ha\c been transported from their source by the 

 winds. 



The arguments used by Matthew to prove that the White River of 

 the plains is not of lacustrine origin do not apply here. 



1. The deposits, especially the finer ones, are commonly distinctly 

 stratified, often thinly laminated, and sometimes splitting into papery 

 shales. Distinctly stratified beds can often be traced for a considerable 

 distance and sometimes they are beautifully ripple-marked. 



2. The fauna is not strictly a terrestrial one. Abundance of fresh 

 water diatoms, mollusca, and fish are found. 



3. The mammalian remains are usually fragmentary, and occur near 

 hills and mountains of older rocks, which evidently formed the shore 

 of the lakes, or border of the marshes, if such existed. 



4. There is no difficulty in conceiving the obstruction of the waters 

 by orographic movements or by lava flows. For example, the Missouri 

 River from the region of Helena northward to Cascade — a distance 

 of about fifty miles — flows through a cailon in the mountain uplift, 

 which here crosses its course. For the first twenty-five miles there are 

 successions of narrow canons and broader semi-circular areas. In the 

 latter are remains of Tertiary deposits, showing that these valleys w^ere 

 carved out during or previous to Tertiary times. But from near the 

 place where Wolf Creek enters the Missouri there is a change, and the 

 river, instead of cutting its way through Palaeozoic strata, has carved 

 a uniformly narrow canon through eruptive rock. Above this long 

 canon we can trace the Tertiary deposits, occupying present and old 

 river valleys up the Missouri and Jefferson rivers without obstruction 

 of the older rocks to the continental divide and boundary line between 

 Montana and Idaho, near the village of Monida. In fact the old river 

 valley undoubtedly passes through the divide into Idaho. 



The occurrence of this great mass of eruptive rock, were it a surface 

 flow, would seem to offer a ready explanation of the occurrence of the 

 fresh water sediments above. But much of the rock is quite coarsely 

 crystalline, as if cooled at a considerable depth. 



It is true that in no place on the mountain sides has the writer 



'The coarser material is evidently either of delta or stream origin. The writer at 

 present sees no reason for believing that any great extent of the deposits is purely 

 reolian. 



