1917] Merriam-Buwalda: White Bluffs of the Columbia 



263 



with the strata of the Ringold in the face of the White Bluffs, 

 strengthens this idea. Unfortunately extensive observations have not 

 been made on the structure of the Ringold over more than a small 

 portion of the area in which it is exposed, so that it cannot be stated 

 with certainty that upturning and bevelling have not occurred in 

 some of its marginal areas. 



Mode of Deposition. — The available data indicate that the Ringold 

 formation was deposited in a basin the walls of which were essentially 

 the Yakima Range on the west, the Saddle Mountains on the north, 

 and the lava plateaus on the east and south. It is probable that the 

 flat area extending east from the White Bluff's and lying about five 

 hundred feet above the Columbia is to be regarded as an undissected 

 remnant of the aggradational surface developed at the close of the 

 period of deposition, and indicates the elevation to which the basin 

 was filled. 



The Columbia cuts through high ranges like the Saddle Mountains 

 instead of flowing around them, and is an antecedent stream in this 

 part of its course ; in pre-Ringold time its channel therefore lay 

 across the area now occupied by these sediments. The presence of 

 the Columbia in this region at the time the sediments were laid down, 

 and the similarity of the sediments to those transported by the stream 

 at the present day, make it probable that the Columbia deposited this 

 formation. Whether the strata were laid down in a lake formed in 

 the course of the stream, or as flood plain deposits, is not certain, 

 as the limited time spent in the area did not permit an examination 

 of the peripheral areas to determine the presence or absence of such 

 evidence as beaches, bars, and other lacrustal features. The muddi- 

 ness of the Ringold sandstones and the sandiness of the clays are, 

 however, to be contrasted with the cleaner strata usually produced by 

 the efficient classifying agencies of lacustral waters. The apparent 

 scarcity or absence of freshwater molluscan remains, usually quite 

 common in lacustral beds, and the presence at different localities of 

 scattered bones of land mammals, also favor the belief that the 

 deposits are largely of flood-plain origin. 



Area. — Without having mapped its boundaries, the Ringold forma- 

 tion appears to the writers to occupy an area of at least 300 square 

 miles, and may extend over 500 or 600 square miles. To the north 

 the beds apparently reach to the lower slopes of the Saddle Mountains. 

 Their eastward limit is not known, but it is certainly several miles 

 to the east of the Columbia. Their southern boundary likewise has 



