EOCENE OF WIND RIVER AND BIG HORN BASINS 723 



These structural depressions, partly inclosed by the Big Horn, Bridger-Owl 

 Creek and Wind River Mountains, were receiving sediments during the Lower 

 Eocene and Lower Oligocene, but since then have been subjected to deep dis- 

 section by streams and wind erosion, exposing sections of the Tertiary filling. 



Non-volcanic sediments predominate in these Tertiary beds, derived in large 

 part from the rocks of the surrounding mountains, shown by the abundant 

 granite, gneiss, and sandstone fragments in the channel sandstones interstrati- 

 fied with the alternately banded red and blue or yellow clays of the Wasatch 

 and Wind River and by the presence of arkoses in the Uinta. Explosive vol- 

 canic eruptions are indicated by a few narrow tuff bands in the Eocene (Wind 

 River), but especially by a great flow of andesitic agglomerate in the Lower 

 Oligocene. Fine, wind-blown silts, highly calcareous marls, and siliceous 

 spring deposits (chalcedony and opal) characterize the Oligocene above the 

 horizon of the volcanic mud flow. 



Suggestions are offered in explanation of the alternation of color bands in 

 the Eocene clays, based on lithologic and paleontological data. 



Early Tertiary orogenic movements, involving renewed uplift of the Big 

 Horn arch, are demonstrated by a great marginal anticline found in the 

 Wasatch and by the numerous sandstone dikes, apparently of seismic origin, 

 contemporaneous with the accumulation of the Wasatch clays. 



Discussion 



Mr. Sinclair replied as follows to a question by Mr. Campbell : The Wind 

 River deposits in the Bighorn Basin (about 325 feet in thickness, so far as 

 now known) overlie the AVasatch with perfect stratigraphic conformity. Their 

 age is definitely determined to be Wind River by the presence of Lamhdothe- 

 riurn, showing that they are to be correlated with that portion of the typical 

 Wind River east of Lost Cabin, which contains the characteristic LamMothe- 

 Hum fauna. 



TWENTY-FOOT TERRACE AND SEA-CLIFF OF THE LOWER SAINT LAWRENCE 

 BY JAMES WALTER GOLDTHWAIT 



iAl)stract) 



Among the raised beaches of the Saint Lawrence Valley investigated by the 

 Canadian Geological Survey last sununer is a great terrace and sea-cliff, not 

 hitherto described. It is unique for its topographic strength and continuity. 

 The terrace has been traced over 200 miles eastward from Quebec and found 

 to maintain a fairly uniform altitude of 20 feet above sealevel. It is believed 

 to be of wide extent. The question is considered whether it records (a) a 

 prolonged halt between two upward movements of the coast since the great 

 "Champlain" submergence; or (&) coastal subsidence of long duration, sepa- 

 rating an earlier emergence, which was rapid and of great magnitude, from a 

 later emergence, which was slow and of relatively slight amount. Correlation 

 with other evidences of post-Glacial subsidence is discussed. The threefold 

 division of post-Glacial time in Scandinavia by Briigger and de Geer is cited 

 as a parallel case, and the bearing of these facts on isostacy is suggested. 



