422 JOURNAL OF THK WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 17 



Informal Communications 

 David T. Day spoke on some substances extracted from oil shale. 

 R. C. Wells spoke on a deposit of aragonite on the inside of a sealed 



glass tube containing a standard sample of sea water. This commimication 



has since been published in the Journal.^ 



Regular Program 



F. C. Calkins: Thrust fatilting in the Cottonwood District, Wasatch Moun- 

 tains, Utah. 



The thrust faults discovered in the Cottonwood district during 1912 by 

 Loughlin and Butler and independently by Hintze dip in general eastward and 

 hence were naturally supposed at first to have been caused by westward over- 

 thrusting. Recent field study, however, has brought out the following facts : 

 (1) The main thrust plane dips westward in part. (2) The eastward dip 

 is in places steeper than it could have been at the time the thrust-faulting 

 occurred, so that some eastward tilting must have taken place; this tilting 

 may well have sufficed to reverse an original low dip to the westward. (3) 

 Most of the drag folds associated with the thrust faults indicate an eastward 

 drag. It is therefore believed that the overthrusting was mainly eastward 

 though a little westward thrusting may have taken place later. 



The Cottonwood district lying at the intersection of the Wasatch and Uinta 

 axes and affected by the stresses that caused the birth of both ranges is a 

 favorable place for determining the position of the overthrusting in the his- 

 tory of the region. The order of the early events in that history is believed 

 to be as follows: 



At the close of the Mesozoic the site of the Great Basin, instead of beinef 

 depressed relatively to the region at the east, was largely dry land, and the 

 site of the Wasatch and Uinta Mountains formed part of an area of sedimen- 

 tation. Deformation of the ofi"-shore sediments began with "Wasatch" fold- 

 ing on north-south axes. This was followed by thrusting of the land mass 

 over the lower basin at the east. Further movement in the same sense 

 caused the thrust faults to be bent into folds whose axial planes lean eastward. 

 The east-west uplift which gave rise to the Uinta Range, and which was ac- 

 companied or closely followed by the intrusion of granitoid rocks under the 

 crest of the Uinta arch, was antedated by the overthrusting and probably 

 by most of the north-south folding that affects the thrust planes. The thrust- 

 faulting can therefore hardly be more recent than the end of the Cretaceous 



Sidney Paige : Interpretation of the Moon craters. 



Kirk Bryan : Mountain pediments. A discussion of the erosion of desert 

 ranges. 



345th meeting 



The 345th meeting was held at the Cosmos Club at 8 p.m., on Wednesday, 

 March 24, 1920. 



Informal Communication 

 Mr. David White exhibited some highly polished chert pebbles found in 

 residual clay of limestone in Missouri. 



Regular Program 

 Leon Dominian: Geography of Asia Minor. (Illustrated.) 

 H. S. Washington: The chemistry of the Earth's crust. (Illustrated.) 

 This paper has been published in full.* 



2 R. C. Wells. This Journal, 10: 249-254. 1920. 



»H. S. Washington. Journ. Franklin Institute. 190: 7.57-815. 1920. 



