NO. 4 PHYSIOGRAPHY OF ROCKY MOUNTAINS LEE 2J 



tions in eastern Utah recognizes near Greenriver the equivalent of 

 the Wingate — called White Cliff in this region by some geologists 

 and La Plata by others ; the Todilto, which is here gypsiferous and 

 contains marine Jurassic invertebrates; and an equivalent of the 

 Navajo, formerly included in the MeElmo of this region. My own 

 observations in southern Utah in 191 7 convinced me that the Ver- 

 milion Cliff and White Cliff sandstones are essentially one great for- 

 mation. There is little difference between them except in color, 

 and this distinction sometimes fails, for in some places the sandstone 

 is all red. Also, while there is often a shaly division, it is not obvious 

 that the shale is at the same horizon in all places. Furthermore, the 

 fossiliferous marine Jurassic limestone and associated gypsum is 

 above the White Cliff sandstone of southern and eastern Utah. 



The possible correlation of Todilto with the marine Jurassic, as 

 indicated in figures 2 and 6, is made on the assumption that there was 

 only one invasion by the Jurassic sea. A suspicion has been enter- 

 tained by some geologists that there were two invasions by this sea, 

 separated by a relatively short interval of time. The Ellis forma- 

 tion in Montana has been regarded as the time equivalent of the 

 Sundance in Wyoming. Recently some of the fossils from these 

 formations have been .critically examined by John B. Reeside, Ti\, 

 who has kindly permitted me to examine his manuscript. He con- 

 cludes that the Ellis is older than the Sundance, the former corre- 

 sponding to the Lower Oxfordian and the latter to the Upper 

 Oxfordian of Fiaug. 1 Another suggestion of two separate invasions 

 is derived from the descriptions by Mansfield and Roundy, 2 who find 

 in southeast Idaho marine Jurassic fossils at two horizons separated 

 by an unconformity and by more than 1,000 feet of unfossiliferous 

 sandstone. 



It seems fairly certain that the limestone and gypsum in northern 

 Xew Mexico which are correlated with the. Todilto formation were 

 deposited in sea water. If Gregory's correlation of the Navajo and 

 Grand Canyon sections is correct, these beds (Todilto) are repre- 

 sented by shaly beds about 1,000 feet below the marine Jurassic of 

 the canyon region. If, on the other hand, there was only one incur- 

 sion of the Jurassic sea it seems probable that the Todilto is equiva- 

 lent to the marine Jurassic beds which overlie the White Cliff, and 

 that the correlation shown in figure 6, page 22, is correct. 



1 Haug, Emil, Text, p. 998. 



2 Mansfield, G. R., and Roundy, P. V., U. S. Geol. Survey Prof. Paper 

 I, p. 81, 1917. 



