DAVIS. — ROCKY MOUNTAIN TERTI ARIES. 359 



the conglomerate but few have been found, and these are more or less 

 worn ; in the clays they are abundant and their articulation, edges, and 

 muscular insertions are sharp and clearly defined. . . . They are found 

 at all horizons in the formation, aud occur buried in the clays or sand- 

 stones or partially weathered out upon the surface" (154). "Fossil 

 wood, leaves, and stems are abundant" (169) in certain strata of South 

 Table mountain. Within the limits of the city of Denver " there was 

 formerly a very good outcrop of Denver sandstones and clays, with cross- 

 bedding structure, and full of plant remains in certain layers. Here, too, 

 occurs a thin local seam of coal. ... In these same strata Mr. T. W. 

 Stanton found some molluscan remains, associated with plants, and a 

 small but perfect crocodile tooth " (193). The fossil mollusca seem to be 

 of lluviatile rather than of lacustrine types. 



Nowhere in this report or elsewhere have I been able to find any 

 discussion of the share that fiuviatile processes may have had in the 

 origin of the formations, otherwise so elaborately described. Hills has 

 suggested that some of the materials may have been brought from the 

 South park region which " then as now, drained into the Denver 

 basin," thus implying river action in the collection of land waste; but he 

 does not directly discuss the condition of deposition, although the context 

 indicates that he accepted the prevalent theory of a lacustrine origin 

 (Proc. Colorado Sci. Soc, iii, 1890, 393-394). Yet to my reading the 

 record of observations on nearly every page of the Monograph suggests 

 that a fiuviatile origin is at least as probable if not more probable than a 

 lacustrine. Conglomerates near the mountains, pebbles aud sands 

 alternating with clays on the plains, cross-bedding and local uncon- 

 formities, standing tree stumps and fossils of large land animals are 

 in my reading all witnesses to rivers rather than to lakes. 



7. Lacustrine and Fiuviatile Quaternary Deposits. — The body of 

 scientific opinion above quoted regarding the interpretation of our west- 

 ern fresh-water Tertiary formations as lake deposits stands in marked 

 contrast to another body of opinion that might be adduced regarding 

 the origin of the Quaternary basin deposits of the same region. The 

 Quaternary deposits that are interpreted as lacustrine are clays and 

 marls, with the addition of the strictly marginal gravels and sands near 

 the shore lines. Mere wedges of gravel between clay and marl beds 

 in the Bonneville basin, wedges that are trifling in volume when com- 

 pared to many Tertiary conglomerates that have been described as 

 lacustrine, are interpreted by Gilbert as indicating a reduction of Lake 

 Bonneville "so far as to bring subaerial agencies locally into play," 



