500 - / HARLEN BRETZ 



held until melting, and (2) the subsequent removal or burial of 

 debris dropped in mid-valleys. 



Many of the bergs were derived from basal ice in the parent 

 glacier. The amount of fine material associated with the bowlders, 

 and the striated faces of many bowlders, makes this clear. 



Practically all of the debris listed in the foregoing catalogue has 

 been derived from rocks of deep-seated origin, indicating the work 

 of glaciers in the heart of an eroded mountain mass. 



The upper limit of the submergence, determined from present 

 data on drifted bowlders, is about 1,200 feet through central 

 Washington. The lower altitudes of the known erratics in Willam- 

 ette Valley may be because the heavy forest above the cleared 

 bottom land conceals higher bowlders. It may also be due to 

 warping in postglacial time along a hinge line approximately 

 coincident with the axis of the Cascade Range. 



Of -shore sediments of the submergence. — It is significant that in 

 the lower valley of Yakima River, Dry Creek, and Cold Creek, 

 considerable silt depoists occur below the upper limits of the 

 erratics. Many square miles are covered by these sediments west 

 of Mabton and south of the Yakima flood plain. Here they are 

 dissected to a subdued badland topography a'nd the erratics are 

 scattered widely over the area: on divides, slopes, and valley 

 bottoms. But the material is incoherent and fails to stand in 

 bluffs, so that one cannot be sure that erratics are inclosed in the 

 silt deposit. It is probable, however, that these deposits are 

 correlative with those in White Bluffs, now named the Ringgold 

 formation, and older than the glacial submergence. 



It is more significant that investigations on water resources in 

 Quincy Valley^ have shown the presence of "Pleistocene lake beds" 

 below 1,200 feet A.T. Wells nearly 300 feet deep do not penetrate 

 through these beds on Morrison Flat, a few miles west of Moses 

 Lake. These sediments consist of clay, silt, and sand, with a few 

 beds of gravel, and contain bones and shells. ''W. H. Dall states 

 that the fossils collected from the lake beds are fresh- water species, 

 all of which are still living and are not older than the Quaternary 

 period.. They are of the boreal type and could have lived in the 

 cold water of a glacial lake."^ Glacial gravels unconformably 



' Schwennesen and Meinzer, op. cit. ^ Ibid., p. 144. 



