216 GEOLOGY OF THE DENVER BASIN. 



parks there exists a formation very similar to the Denver beds, which lias 

 also been classed with the Laramie. It seems probable that the two forma- 

 tions were laid down almost contemporaneously. If the two series be con- 

 sidered as of the same age, the evidence of the Middle Park beds strongly 

 confirms the deductions made from the Arapahoe and Denver formations 

 concerning geologic events in the epochs immediately succeeding the 

 Laramie. 



No strata corresponding to the Arapahoe have yet been found beneath 

 the Middle Park beds, but they may well exist in places not yet carefully 

 examined. The folding and great erosion which preceded the Arapahoe 

 on the eastern side of the mountains are paralleled by the elevation and 

 degradation which succeeded the uppermost member of the conformable 

 Cretaceous series in Middle Park, preparing the surface on which the tuffs 

 and conglomerates rest. The material of the latter was manifestly derived 

 from a great series of volcanic eruptions similar in character and variety to 

 those assumed for the slope adjacent to the Denver sea. Whether the thick- 

 ness of the Middle Park beds lie taken at 3,000 or 6,400 feet, they testify 

 to a long epoch of gradual subsidence contemporaneous with deposition. 



strata near canyon. — In his cited address Mr. R. C. Hills referred to rem- 

 nants of a formation resembling the Denver beds that occur south of the 

 Arkansas River in the vicinity of Canyon, Colo. Directed by information 

 personally given bv .Mr. Hills, Mr. Eldridge examined the district and 

 found apparent equivalents of both Arapahoe and Denver beds. The ana- 

 logue of the former is a heavy conglomerate, resting upon the Laramie, 

 upturned with it in the foothill section, but exhibiting among its pebbles 

 fragments recognized by Mr. Eldridge as derived from the Niobrara and 

 Dakota Cretaceous and from the Jura. These tell the same story of uplift- 

 ing and erosion which is contained in the Arapahoe conglomerate. 



The formation resembling the Denver beds is made up of a variety of 

 andesitic rocks and is lithologically almost identical with the formation 

 named. 



No fossils have been found in either of these formations, but their 

 occurrence is noteworthy in connection with others. If they belong to the 



