292 



University of California. 



[Vol. 2. 



Cove, and overlying what is probably Middle John Day on Pine 

 Creek, about three miles northwest of Spanish Gulch. 



The tuffs and ashes seem in some cases to have been worked 

 over somewhat by air or water. At other points, beds many feet 

 thick have apparently been deposited directly, without much, if 

 any, working over by either wind or water. 



The source of the ash and tuff is as yet unknown. It probably 

 came from vents not very distant from this basin of deposition. 



Excepting the beds of sand and gravel near the top of the 

 section, the stratification throughout the whole thickness of the 

 John Day is very regular. Numerous beds of almost pure ash or 

 tuff compose uniform, hard, and prominent layers, between which 

 in the softer beds the regular deposition of thin layers is plainly 

 indicated by delicate variations in color. Nodular layers, possibly 

 produced in part by contained organic remains, are not infrequent 

 in some localities, and small nodules are usually scattered through 

 a large part of the Middle John Day. 



The erosion forms and coloration of the John Day strata are 

 quite characteristic when compared with those of other formations 

 in the basin. In general the beds are colored various shades of 

 red, green, blue, or yellow. In some cases they are white or gray. 

 As will be shown later, the coloration is an important character in 

 distinguishing the subdivisions of the system. The beds are 

 usually quite soft and disintegrate very rapidly, forming a layer of 

 mud several inches thick over a large part of the exposed surface. 

 A moderately heavy rain starts the mud almost in streams, and, as 

 it is soon formed again, erosion must proceed very rapidly. At 

 several localities visited by the writer, groups of unrelated bone 

 fragments, evidently brought together by collectors, were found 

 resting on small pinnacles several inches in height, showing that 

 in ten to twenty years erosion had progressed at least four or five 

 inches in fairly favorable localities. 



In the Lower John Day the tendency of erosion is almost 

 always to produce dome-like, mud-covered hills, with scarcely a 

 fragment of the bed-rock protruding anywhere. In the middle 

 division steep, pinnacled bluffs, exhibiting beautifully the typical 

 bad-land structure, are common, and in the uppermost division 

 they are the rule. 



