FORMATIONS OF THE FRONT RANGE 425 



marine Jurassic is represented, I feel certain that all those in the Front 

 range are of Morrison age. 



MORRISON FORMATION 



This formation extends along the entire Rocky Mountain front through 

 Colorado, outcrops frequently, and presents very characteristic features. 

 At a very few localities it is cut off by faults or locally buried under 

 overlaps of younger formations. It is also exposed in some of the can- 

 yons eastward, notably in the deeper ones of eastern Las Animas count} T 

 and in the Two Butte uplift. Its general character is nearly uniform 

 throughout, a series of light colored, massive clays, "joint clays," with 

 thin beds of limestone and sandstone of fresh water origin containing 

 bones of saurians of the so-called *' Atlantosaurus " fauna. Its thickness 

 averages less than 200 feet in most cases. It presents frequent and rapid 

 variations in the local succession of beds, but the predominance of joint 

 clays of chalky aspect and the occurrence of maroon and purplish layers 

 among them are characteristic features. The name Morrison was given 

 by Eldridge from the town of Morrison, where the formation is exten- 

 sively developed. South of the end of the marine Jurassic deposits 

 (Sundance formation) the Morrison beds lie unconformably on the 

 Chugwater formation for many miles, and southwest of Colorado Springs 

 overlap the Red beds of the Fountain and Badito formations. In east- 

 ern Las Animas county they lie on a bed of gypsum. Mr W. T. Lee 

 has traced them into western Oklahoma and found that they either 

 merge into or take the place of the marine beds of the upper formations 

 of the Comanche group in the Lower Cretaceous, a relation which I 

 have found also near Two buttes, on Butte creek, in Prowers county, 

 Colorado. The saurian remains which have been obtained so abun- 

 dantly from the Morrison beds west of Denver and north of Canyon City 

 are regarded as latest Jurassic by some paleontologists and earliest Cre- 

 taceous by others, but from the stratigraphic relations of the formation 

 to the Comanche it is preferable to class it in the Lower Cretaceous. 



The basal unconformity is one of widespread planation, with local 

 shallow channeling but no perceptible discordance of dips. The follow- 

 ing section of the Morrison formation was measured northwest of Laporte, 

 Colorado : 



Feet 



" Dakota". .Coarse sandstone, with conglomerate at base 



f Gray massive shales, with thin limestone bed about 20 feet below 



Morrison..] to P 80 



Limestone, gray, with algae 6 



t Sandy shale, reddish to buff, partly massive 20 



Pinkish and bnff sandstones at top of Red beds. 60 



