MOOE, STUDY OF THE MORRISON FORMATION 



123 



fine granular calcite and other carbonates. Mixtures of this kind com- 

 prise a large proportion of the formation. 



Fine calcareous sandstones are very common and occur in thick beds. 

 They consist typically of fine angular quartz with a matrix of fine 

 granular calcite and probably dolomite and siderite. They grade into the 

 clays through varieties with more kaolinic matter, and into the limestones 

 through members with less quartz. They also grade into arkoses through. 



Fig. 88. — Calcareous arkosic sandstone^ from the lower heels of the Morrison formation 

 at Garden Park, Colorado. 



The clear light and dark grains are quartz ; the interstitial material is calcite ; and the 

 banded grains are plagloclase feldspar. About 28 X. (Crossed nicols.) 



fine sandstones in which feldspars occur. The latter are especially 

 abundant in the lower beds of the formation. The calcareous sandstones 

 also grade into quartz sandstones through varieties with less calcite and 

 more quartz. 



The limestones are usually only a foot or two in thickness. They vary 

 from practically pure carbonates to siliceous and argillaceous varieties. 

 Small molluscan fossils are sometimes present. 



