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ANNALS NEW YORK ACADEMY OF SCIENCES 



Calcareous nodules and concretions often form beds amidst less cal- 

 careous sandstones or clays. 



The coarser sandstones vary from nearly pure quartz sands to highly 

 calcareous and arkosic members. One of the typical coarser sandstones 

 is that in which the dinosaur bones occur in the Marsh-Hatcher quarry 

 near Canon City, Colorado. This sandstone consists largely of medium- 

 sized to large quartz grains, often well rounded, with finer angular quartz 



Fig. 89.^Calcaieoiis argillaceous sandstone, from the Morrison formation near Ganoh 



City, Colorado. 



The light grains are quartz ; and the dark interstitial material is mixed carbonates and 



clay. About 28 X. 



grains scattered among them. Feldspars are fairly abundant and often 

 of large size. Volcanic ash grains occur, some of which are perfectly 

 fresh, others being altered to masses of granular quartz. Calcite, and 

 probably some dolomite, occurs in the interstitial spaces. Some of this is 

 granular and some of it is coarsely crystalline. 



Coarse, round-grained sandstones of this type often show seolian cross- 

 bedding. 



