THE RED BEDS OF COLORADO 205 



Interpretation: the writer's upper-delta hypothesis. — If it is diffi- 

 cult to see why the hypothetically marine sands of the Lyons are 

 pink to red, it is more difficult to picture deepening waters depositing 

 yet redder sediments. It would be daring, indeed, to assmne that 

 the present red of these sands and shales was caused by later dehy- 

 dration of originally gray-green sands; yet, if the western land was 

 now in its last stages of degradation and furnishing primarily red 

 material, why was not the red matter chiefly mud ? Incidentally, 

 could not invertebrates live in the deepening sea? Marine shale 

 usually preserves traces of life, and, though shale is not predom- 

 inant in the Lykins, it is nevertheless abundant. 



Without directly objecting further to the marine hypothesis, 

 is it not more plausible that in early Lykins time climatic condi- 

 tions changed, so that the desert slowly became a flood plain or the 

 upper reaches of a delta ? There may have been elevation to the 

 west, though the Lykins sediment is as fine grained as the Lyons; 

 there may have been increased rainfall in that region; there may 

 have been solar fluctuations; there may have been an advance of 

 the eastern waters. In any event, the sediments, in many ways, 

 resemble those of the upper stretches of a delta. Already in the 

 lower beds mud lumps begin to appear, and whence arise mud 

 lumps if not from river action? The green splotches and lenses, 

 too, first appear in the lower Lykins. The coloring matter of these 

 green blotches is revealed by analysis as ferrous iron. It would 

 seem unlikely that green was once the prevailing color of sediments 

 now so red. Far more likely it would seem that the blotches are 

 probably due to the reduction of ferric iron, and the most natural 

 reducing agent would be the carbonaceous matter found here and 

 there on the supposed delta. Frequently characteristic of a delta, 

 also, is the change of red sandstone into green shale within the space 

 of a few feet horizontally. Amphibian tracks, too, have been found. 



Occasionally, in the time required for the deposition of the 

 Lykins, a sea might have advanced on a delta. Such may be the 

 explanation of the "crinkled" bed, which always occurs near the 

 base of the Lykins. If it were due to a north- south stress in Cre- 

 taceous time, as stated by Fenneman^ and others, strata above and 



' N. M. Fenneman, op. cit., p. 26. 



