MORRISON AND SUNDANCE FORMATIONS 251 



In regard to the contacts above and below the Sundance, Darton® re- 

 marks as follows : 



"Although there is a long time interval between the Sundance and Chug- 

 water [Triassic] formations, marked erosional unconformity is rare and in 

 places it is difficult to draw the line between them. This is probably because 

 the first sediments of the upper formation were derived from the one below. 

 The upper limits [of the Sundance] are similarly ill defined. There is no dis- 

 cordance in dips of underlying or overlying formations." 



Lee' observes that 



"in most places the bedding planes of the Morrison are so nearly parallel with 

 those of the formations above and below it that the structural relations can 

 only be apprehended by taking a broad vieM^ ... In strong contrast with 

 the unconformable relations at its base, the Morrison is obviously conformable 

 with the beds above it. . . . There is no escape from the conclusion that 

 the Morrison, as a formation, is structurally much more closely related to the 

 overlying formations of Cretaceous age than it is to underlying formations." 



In the opinion of Stanton,^ 



"the lithologic and stratigraphic evidence of a break in sedimentation is fully 

 as great, if not greater, between the Morrison and the rocks of Washita age, 

 where they are in contact, as it is between the Morrison and the Sundance in 

 the northern area where these two formations come together." 



Mook*^ now also regards the Morrison as an overlapping formation. 

 There is an "erosion plane beneath the Morrison over most of its area," 

 and the formation "is more closely related to the overlying than to the 

 underlying formations." He concludes : 



"It appears, then, that the Morrison commenced as a continental deposit in 

 the western areas of its occurrence in early Comanchian time (or possibly 

 latest Jurassic), and that it spread outward as it was built up, the uppermost 

 and easternmost beds being laid down in [later] Comanchian time. ... It 

 seems probable that the Morrison merged into the marine [Comanchian] de- 

 posits" in the southeastern and eastern areas. 



Description of typical Sundance and MoiirasoN Si^otions 



GENERAL REFERENCE 



The following sections of the Morrison and Sundance formations are 

 given to bring out the detail of the stratigraphy and the variability of the 



" N. H. Dartoii : I'aleozoii; aud Mesozoic of central Wyoming. P.ull. (Ji'ol. Soc. Am., 

 vol. 19, 1908, p. 438. 



'' Op. cit, pp. 309-.S10. 



8 T. W. Stanton: Inverlel)rale fauna of the Morrison formation, null, (!('(»l. Sin-, Am,, 

 V9I. 26, 1915, p. 348. 



"Op. cit., pp. 160, 172. 



