MOOK, STUDY OF THE MORRISON FORMATION 121 



The first variety of sediment to be considered is the fine hematitic 

 sandstone. As this is composed largely of fine angular quartz grains, it 

 will be spoken of as a grit. This grit is usually more prominent in the 

 upper members of the formation in any given locality, but also occurs in 

 smaller amount near the base. In the field it is reddish to chocolate 

 brown in color. In thin section, seen with reflected light, it is red. The 

 principal mineral constituent is quartz, in small grains. The interstitial 



Fig. 86. — Argillaceous limestone or calcareous clay, from the loiver part of the Morrison 

 formation near MacJc, Colorado. 



About 28 X. 



material is clayey matter stained to a bright red by hematite. The origin 

 of this hematite will be discussed below. The relative proportions of 

 quartz and hematitic matrix vary greatly. 



This red quartz grit grades into fine calcareous sandstone tlirougli fine 

 sands with the interstitial matter partly stained by hematite and partly 

 made up of fine-grained carbonates. It also grades into the true clays 

 through members with a similar amount of quartz and a considerable 

 amount of kaolin. Such a type occurs near the top of the Garden Park 



