AGE OF THE ARAPAHOE AND DENVER. 215 



of types identical with those in the Denver formation. 'These beds are 

 coarser in texture and are laterally more variable than the Denver strata, 

 but resemble them very much in many details. The sharp line drawn by 

 Marvine between tin- "breccia" and his "Lignitic" series does not appear 

 justifiable. While Marvine does not refer to volcanic materials in the upper 

 series, there is in fact a gradation between the lower, dark, almost purely 

 andesitic strata ami the lighter-colored beds above, in which granitic debris 

 usually predominates, although micaceous and horublendic andesites are 

 abundant for more than 2,000 feet upward in the series — as far as the 

 writer's observations go. 



Plant remains are the only fossils as yet known from the .Middle Park 

 strata. These were found by the Ilayden survey party in the "Lignitic" 

 series only, but they occur also in the dark tuff layers of the lower beds. 

 A number of the species described by Lesquereux as from Middle Park are 

 now known to have come from the Eocene lake bed at Florissant, Colo. 

 The entire known fossil flora of the Middle Park series has been studied by 

 Mr. Knowltou, and the result will appear in his forthcoming monograph on 

 the Laramie and allied floras. It is sufficient to say here that twenty-five 

 satisfactory species are known from these strata, and that by far the 

 Strongest alliance is with the flora of the Denver formations. 



Along the Grand River near Hot Sulphur Springs the stratigraphic 

 relations of the Middle Park beds are clearly shown. They here rest upon 

 the upturned and eroded section of the Mesoxoic series, from the Jura to 

 the Fox Hills, and overlap the former to the granite. No Laramie is here 

 seen, whether from erosion or nondeposition is not definitely shown, but 

 from the fact that coal-bearing strata are present in North Park it may be 

 inferred that the Laramie once existed in Middle Park, but was entirely 

 removed by the erosion preceding the deposition of the Middle Park beds. 



It is not definitely known at present whether the entire thickness of 

 6,400 feet of strata — taking Marvine's measurement — belongs in fact to one 

 formation, but no reason for doubting this has appeared as yet. For nearly 

 3,000 feet the series is certainly one, lithologicallv. stratigraphically, and 

 in its fossil plants. 



From the foregoing statements it appears that in Middle and North 



