120 



ANNALS NEW YORK ACADEMY OF SCIENCES 



forming many intermediate varieties. Other types are also present, but 

 in minor amounts. 



The most characteristic beds in the Morrison are tlie so-called "joint- 

 clays." These are fine sediments which have the appearance of clay, and 

 which weather into clays. They are variegated in color, and have been 

 the cause of the name "variegated beds" formerly applied to the forma- 

 tion. These "joint-cla^-s" are composed of a variety of sedimentary types, 



Fig. 85. — Fine grit, from near the top of the Morrison formation at Garden Park, 



Colorado. 



The light grains are quartz ; the light patches are holes in the slide ; the dark patches 

 are limonite. About 28 x . 



more or less distinct from each other in character, though there are often 

 gradational varieties. This variety of elements is responsible for the 

 variegated color. The sediments which make up the "joint-clays" are : 

 fine-grained hematitic sandstones or grits; true kaolinic clays; fine cal- 

 careous sandstones; siliceous limestones; and argillaceous limestones. 

 Intermediate or compound types are also abundant. 



