MOOK, STUDY OF THE MORRISON FORMATION m 



"formations, of Permian, ? Pennsylvanian and Devonian ? age respectively 

 (Cross and Larsen, 1914, 7) ; and in still other areas on pre-Cambrian 

 ■crystallines. In northwestern Utah, near Vernal, the non-marine portion 

 •of the Flaming Gorge formation, equivalent to the Morrison, rests on 

 marine beds of upper ' Jurassic age, containing Pseudomonotis curta, 

 •etcetera. The contact is apparently conformable, no sudden change in 

 lithological characters being observable. 



In the areas of Morrison outcrops in Montana, and in most of those 

 in Wyoming, the formation rests on the Sundance or corresponding beds. 

 'These beds have been determined by Stanton (1909, 9) to belong to the 

 lower jDart of the upper Jurassic. In certain areas in Montana there is 

 ■evidence of a pre-Sundance erosion plane. The contact between the 

 Morrison and Sundance formations is sharp in some places, while in 

 •other places it is obscure. 



In general it appears that there was a slight break between the Morri- 

 ■son and Sundance formations, but not one of any considerable extent. 



In the Black Hills area the Morrison usually lies on the Sundance beds, 

 ■often with a sharp contact. In some localities, however, the Morrison is 

 .separated from the Sundance by the Unkpapa sandstone, indicating an 

 interval between the retreat of the Sundance sea and the beginning of 

 Morrison deposition. 



In eastern Colorado the Morrison rests on Sundance beds near the 

 Wyoming boundary. Throughout most of the area in eastern Colorado 

 :and New Mexico the Morrison rests on Eed Beds of various ages. In 

 the northern half of Colorado, except at the extreme northern end, the 

 Morrison lies on the Chugwater Eed Beds. At Morrison the formation 

 is separated from the Eed Beds by a white sandstone of unknown age. 

 At Colorado City a bed of gypsum lies between the Morrison and the 

 Eed Beds. Farther south in Colorado the Morrison rests on the Foun- 

 tain or Badito formations. South of Beulah, in southern Colorado, the 

 Morrison rests directly on the crystallines. In northeastern ISTew Mexico 

 the Morrison is underlain mostly by Eed Beds, which have been warped 

 ^nd eroded before the deposition of the Morrison. N^ear Exeter there is 

 a distinct sandstone formation between the Morrison and the Eed Beds. 

 'The uppermost members of the Eed Bed series often consist of gypsum in 

 this area. 



It is seen from the above description that there is a widespread erosion 

 plane beneath the Sundance formation in some areas, and there is evi- 

 •dence of a slight break between the Morrison and Sundance formations. 

 Is the pre-Sundance erosion plane to be correlated with the pre-Morrison 

 plane, which is observable where the Sundance is absent, or is the pre- 



