THE RED BEDS OF COLORADO 197 



evidenced in miniature floods, is the production of much " scour and 

 fill" cross-bedding, which is of medium scale and parallel to the 

 dip of the true bedding, as in the Fountain sediments. In addition, 

 as the flood subsides, there arise little islands, separated by unorien- 

 tated rivulets. The dip of deposits on these islands and temporary 

 "shores" is at all angles and in all directions, even contracurrent, 

 again as in the Fountain sediments. 



Interpretation: climate and paleogeography. — Can the type of 

 river sedimentation be further determined ? It is believed that it 

 can — by consideration of climatic and paleogeographic possibilities 

 such as should not be ignored in modern studies. Almost certainly 

 the climate can be set down as semiarid, with all that that implies. 

 As to paleogeography, the marine h5rpothesis assumes, as has 

 been said, that directly to the west of a shallow sea-trough lay 

 land of unknown extent. The writer also thinks that the ancient 

 Colorado rivers must have flowed from either the west, northwest, 

 or southwest. The basis of belief is not the time-worn statement 

 that the sediments are those which would have been derived from 

 a granitic mass similar to that west of the present-day foothills. 

 That argument is not convincing. But, if the sediments came from 

 north of Colorado or east, they should have been coarser in those 

 directions. To the east. Fountain material seems entirely lacking.^ 

 To the north, the presence of the intercalated limestones carrying 

 marine fossils reveals a sea, strait, or bay in that direction.^ 



It is then quite possible that streams flowing almost east from 

 a Paleozoic Front Range furnished the Fountain material; if so, 

 the Fountain is an ancient Piedmont plain, with here and there 

 alluvial fans higher than elsewhere, and with masses of sheet wash. 

 The nature of the sediments fits in with this idea. Furthermore, 

 since the Maroon conglomerate and other West Slope series seem 



' In western Kansas, the Cimarron shale, 1,000 feet thick, lies unconformably on 

 granite, but it would seem to correspond to Lykins material in Colorado. In any event, 

 it is far finer grained than the Fountain; the same is true of what may be 1,000 feet of 

 Foimtain sediment in the Purgatoire Canyon south of La Jimta (maximum size of 

 pebbles 2 inches). See also N. H. Darton, on the Cimarron shale (Syracuse-Lakin 

 folio, p. 2). 



^ The writer believes, because of studies made in Wyoming, that a strait coimect- 

 ing with a western sea lay between Colorado and a Wyoming land mass. 



