Calkins. j Petrography of the John Day Hay in. 171 



question and have brought out clearly the fact that the fossils of 

 these beds are terrestrial, to the total exclusion of aquatic forms. 

 Matthew, who advocates the theory of aeolian origin for the White 

 River Beds, emphasizes the absence of lamination in those rocks, 

 and the failure of shore features at their contact with older 

 formations. Let us consider what light our petrographic studs- 

 has thrown upon this problem. 



The fact of the great preponderance of pyroelastic material in 

 the tertiary , beds of Eastern. Oregon, recognized to a certain 

 degree in the field, has been demonstrated by laboratory study. 

 This very fact throws a burden of proof upon any advocate of 

 the lacustrine hypothesis. If the material is not detrital there is 

 no presumption in favor of the supposition that it was laid down 

 by water unless it is shown to have the structural characters of 

 water- laid deposits. 



They do not, in the opinion of the writer, possess those 

 characteristics. In materials like the John Day tuff, comprising 

 fragments so different in density as augite crystals and highly 

 vesicular pumices, descending through any considerable depth 

 of water, a sorting action would be exerted and produce lamina- 

 tion. The upper portion of a stratum deposited in a single 

 shower would be composed mainly of the lighter fragments and 

 the base mainly of the heavier fragments. No such lamination 

 was observed. Where a layer of tuff is distinguished by difference 

 of color or hardness from those immediately above and below, it 

 is found to be homogeneous from top to bottom. It appears to 

 the writer that the regularity of the strata on a large scale 

 would be characteristic of material falling from widely spreading 

 clouds of volcanic ash. 



The "red beds" of the Lower John Day deserve a paragraph 

 of special comment. The deep brick color of these rocks is due 

 to their impregnation with ferric oxide. The peroxidation of 

 this iron must have been a secondary process which must neces- 

 sarily have taken place before the material was deeply buried 

 beyond contact with atmospheric influences, and which could not 

 have been accomplished under water. It is believed, then, that 

 the early John Day was a period when thin showers of ash were 

 falling with intervals generally long enough to allow of oxida- 



