ABSTRACTS OF PAPERS 6i 



The Dalles beds, in Oregon, immediately east of the Cascade Range, are 

 thought to be made up of two different formations, the lower of which is a 

 phase of the Satson formation and the upper a post-formation deposit of vol- 

 canic ejectmenta of local origin and small extent. 



A sedimentary deposit about Arlington, Oregon, and Roosevelt, Washington, 

 50 miles east of the Dalles, is believed to be an eastward continuation of the 

 lower part of the Dalles beds and to represent the Satson formation. It has 

 yielded vertebrate remains. 



Another sedimentary deposit in this locality is probably correlative with the 

 Mascall and Ellensburg formations, of Miocene age. 



Two drainage courses of the Satson epoch are thought to be traceable west- 

 ward to a confluence near Lyle, Washington, on the eastern slope of the Cas- 

 cade Range. One is followed now by Columbia River for about 100 miles 

 above the Dalles, the other crosses several anticlinal uplifts between Lyle and 

 Priest Rapids, 90 miles to the northeast, and lies at right angles to the course 

 of Yakima Valley. 



There are only three post-deformation water-laid deposits in the valley above 

 the present floodplain : (1) the upper part of the Dalles beds; (2) gravel ter- 

 races whose grade rises about two and a half feet per mile from the Portland 

 delta (altitude, 300 feet above tide) eastward for at least 150 miles, and (3) 

 berg-borne erratic material throughout the full length of the valley here dis- 

 cussed (upper limit, about 1,250 feet). All are of Pleistocene age, 1 being the 

 oldest. The relative ages of 2 and 3 are not yet known. 



Presented without noteS;, with lantern-slide illustration. 



EVIDENCES OF AN UNCONFORMITY WITHIN THE PRE-CAMBRIAN OF THE 

 BLACK HILLS OF SOUTH DAKOTA 



BY J. J. BUNNER ^ 



(Abstract) 



Field studies in the northeastern portion of the pre-Cambrian area of the 

 Black Hills of South Dakota have furnished evidences of the existence of a 

 hitherto unknown unconformity that separates the pre-Cambrian of that re- 

 gion into two divisions of the probable rank of systems. The older system of 

 sediments outcrops within an oval area approximately three miles by two 

 miles in extent and occupies the center of a slightly elongated domical struc- 

 ture. The intrusion of igneous rock into both systems is thought to have had 

 an effect in producing the structure. Large masses were intruded near the 

 center of the dome and along the western flank, where there appears to be a 

 large fault. 



The older formation comprises quartzites, quartz-sericite schist, and iron 

 formations consisting of alternate bands of quartz and specular hematite or 

 magnetite. Completely surrounding this older system is a younger one, com- 

 posed of conglomerates, quartzites, iron formations, limestones, and various 

 schists and slates. The contact between the two is, in places, clearly an ero- 

 sional one. The basal member of the younger system is generally a conglom- 



' Introduced bj' George F. Kay. 



