18 Veatch — Definition of the Geologic Term Laramie. 



Akt. II. — On the Origin and Definition of the Geologic 

 Term Laramie* ; by A. C. Veatch. (An Abstract.) 



Investigations of the United States Geological Survey 

 during the summer of 1906, covering the larger part of the 

 Laramie exposures on the Laramie Plains, examined by the 

 King and Hayden surveys, have revealed many new and impor- 

 tant facts bearing on the Laramie problem. 



By detailed areal surveys it was found : (1) That the ligni- 

 tiferous series which in the Laramie Plains lie between the 

 Montana below and the Fort Union above, and has a maximum 

 thickness of about 12,500 feet, is divided about the middle by 

 an unconformity ; (2) that this unconformity is in the same 

 stratigraphic plane and continuous with the unconformity 

 which in the vicinity of Carbon and to the southeast separates 

 all the Laramie beds, studied by the Hayden and King parties, 

 from the underlying Cretaceous ; (3) that the beds above the 

 unconformity rest, often with great divergence of dip, on all 

 the underlying beds down to and including the Dakota ; (4) 

 that the basal conglomerate, locally well developed at the 

 horizon of the unconformity, while composed largely of mate- 

 rial derived from the underlying Cretaceous rocks, notably the 

 Benton, contains pebbles and bowlders from the pre-Cambrian 

 crystallines now exposed in the hearts of the surrounding 

 ranges. This unconformity thus involves the total thickness of 

 the Cretaceous portion of the beds below the unconformity, 

 and probably the whole sedimentary series of this region, or 

 over 20,000 feet of strata. 



The Laramie Plains section in brief is as follows : 



Generalized section of the rocks of the western part of the 

 Laramie Plains in Carbon County, Wyoming. 



Feet 

 North Park Tertiary 4,500 -f 



Fort Union .1 800-2,000 



" Upper Laramie " 6,000 



Unconformity .-^.-^.-^o-w..-^~-«~..-w«~«~..-w«»^. 



"Lower Laramie " . 6,500 



( Lewis ) "Fox Hills" of the early j 3,000 



Montana 4 Mesa Verde ) surveys ( 3,200 



( "Pierre shale "f ..-. 3,500 



* Published by permission of the Director of the United States Geological 

 Survey. This subject is discussed in full in the Journal of Geology, No. 5 

 (July-August). 



fit is the belief of Dr. T. W. Stanton that the Mesa Verde and part of the 

 Lewis also belong to the Pierre, as that formation is developed east of the 

 Rocky Mountains. A local name will therefore be applied to this lowest 

 division of the Montana in this section. 



