MORRISON FORMATION. 01 



The marls are green, drab, or gray, and can - ) in the lower two-thirds 

 numerous lenticular bodies of limestone of a characteristic drab color and a 

 texture compacl and even throughout. A sm;ill bul persistenl band of sand- 

 stone and limestone in thin alternating layers occurs aboul 20 feel above the 

 base; in some places the arenaceous elements largely predominate, and near 

 Mount Vernon, 3 miles north of Morrison, and in the vicinit) of Van Bibber 

 ( Y< •(•!<, there are at aboul this horizon from 1<> to 1 "> feel of dull-graj or ye\-* 

 lowish sandstones carrying small pebbles of flint of various colors. The clays 

 of the lower two-thirds of the Jura are remarkable for their reptilian remains, 

 and from the predominating form have been designated "Atlantosaurusclaj s." 



The upper third of the Jura is generally a succession of sandstones 

 and marls, of which 1 1 1 « - former predominate; locally, however, either may 

 prevail to almost the entire exclusion of the other. The most important 

 sandstone occurs just above the Atlantosaurus clays, is very persistent, and 



from contained Saurian remains has been called the Saurian sandst ■. It 



varies in thickness between 5 and 35 feet, and in its distance below the 

 Dakota from lo to L25 feet, although more generally from 50 to 80 feet. 

 The chief constituent is quartz. The sandstone is everywhere marked with 

 small rusty dots sharply defined and round, one-sixteenth to one-fourth inch 

 in diameter, the resull of spherical stains of brown oxide of iron; occasion- 

 ally the appearance is one of irregular mottling. The sandstone b locally 

 divided into several layers by narrow intercalations of drab claw In the 

 vicinity of Turkey ('reek these clays reach the unusual thickness of '-''i to 

 :iu feet, the >andst ss aggregating about 20 feet. The bed may be locally 



calcareous, especially in the northern half of the field, the lime being 



uniformly distributed throughout the mass. At the base is generally a 

 conglomerate, of a maximum thickness of 8 feet, in which the pebbles so 

 closely resemble those of the Dakota that. bu1 lor a slight admixture of red 

 jasper and the characteristic la-own dots, the two layers coiil. I with difficulty 

 he distinguished from each other. The shales overlying tin- sandstone are 

 similar to those comprising the bulk of the Jura, hut cany through them a 

 number of minor sandstones and occasionally one or two strata of limestone. 

 A variation in the Saurian Bandstone occurs in the vicinity of Van 

 Bibber Creek, which, on account of its determinative value in connection 

 with the structural features about Golden is of considerable importance. 



