THE COMANCHE AN PERIOD 121 



It is not easy to see why fossils of plants and land animals should 

 be so widely distributed, both vertically and horizontally, in a lacus- 

 trine formation, though their wide dissemination in a region of land 

 deposits would be readily understood if the region were flat and sub- 

 ject to aggradation. The leg-bones of large land animals (dinosaurs) 

 are frequently found upright, or inclined at some considerable angle 

 to the bedding planes, as if the animals had been mired. Some 

 of the bones of the Morrison beds are said to be in such condition as 

 to show that they were exposed and partly decayed previous to their 

 burial. In other cases, one end of a bone appears to have undergone 

 subaerial decay, while the other was preserved. If one end was sunk 

 in mud while the other was exposed, as might be in marsh or fluviatile 

 deposits, this phenomenon would be explained. In the Black Hills 

 region there are some beds of limestone composed largely of the secre- 

 tions of fresh- water algae. 1 



The position of these formations in reference to the Rocky 

 Mountain axis is much the same as that of the Potomac to the 

 Appalachian axis, and the same conception as to the mode of origin 

 may be entertained. This involves some lacustrine 2 or quasi-lacus- 

 trine deposition, combined with fluvial and sheet wash aggradation. 

 The extraordinary thickness assigned to some parts of the Kootenay 

 formation (7000 feet) is scarcely credible under any hypothesis, except 

 as interpreted on the principles of oblique deposition and subsequent 

 thickening by shear and mashing. 



It is not now possible to correlate the Kootenay formation with 

 the Morrison, nor is it possible to correlate either the Kootenay or 

 the Morrison with the Potomac, the Tuscaloosa, or the Comanchean 

 of Texas; but, except perhaps the Kootenay, the other series are thought 

 to correspond approximately with the Trinity of the Texas region, 

 and with the lower part of the Potomac. The difficulty in the correla- 

 tion of these formations with those of the coastal regions lies in the 

 facts (1) that they nowhere approach each other, and so have no 

 stratigraphic inter-relations, and (2) that there is no reliable standard 

 with which they may be separately compared. 



Between Kansas and the Black Hills of South Dakota, Lower Cre- 



1 Darton and Smith, Edgemont, S. D.-Neb. folio, U. S. Geol. Surv. 

 2 Dawson, loc. cit. 



