34 GEOLOGTCL FORMATIONS 



The " Third " Magnesian limestone has long been regarded 

 as the lowest number of the series exposed over a greater por- 

 tion of the Ozark uplift. It is a buff, rather compact dolomite, 

 heavily bedded, with occasional chert layers, and is estimated 

 to have a maximum thickness of about 400 feet. 



Swallow's description of the " Second " sandstone is as 

 follows: "It is usually a brown or yellowish brown fine- 

 grained sandstone, distinctly stratified in regular beds, vary- 

 ing from two to eighteen inches in thickness. The surfaces 

 are often ripple-marked and micaceous. It is sometimes quite 

 friable, though generally sufficiently indurated for building 

 purposes. The upper part is often made up of thin strata of 

 light, soft, porous, semi-pulverulent sandy chert or horn-stone, 

 whose cavities are usually lined with limpid crystals of quartz. 

 Fragments of these strata are very abundant in the soil and on 

 the ridges where this sandstone forms the surface rock. It 

 sometimes becomes a pure white, fine-grained, soft sandstone." 

 Thickness 50 to 100 feet. In portions of the rock are found 

 chert bands containing imperfect fossils. 



The " Second " Magnesian limestone is exposed in a broad 

 belt around the Ozark uplift. It reaches a thickness of over 

 150 feet in places. Lithologically it is very much like the other 

 limestones of the series, being composed chiefly of buff mag- 

 nesian beds, usually fine-grained and compact in texture. Often 

 there are intercalated layers of chert, sandstone or earthy lime- 

 stone. Broadhead has regarded this formation equivalent to 

 the Calciferous sandrock of New York ; but the fossil remains 

 thus far found are far too meager to enable its fauna to be made 

 out with any degree of certainty. The character of the rock 

 is well shown in the gorge of the Missouri, from Jefferson City 

 many miles down the stream. (Plate i.) 



In lithological characters the First or Saccharoidal sand- 

 stone is a white, fine-grained, homogeneous rock, very pure, fri- 

 able, but withstanding the weathering influences in a remarkable 

 manner. Locally it has a small percentage of iron, turning the 

 stone to a brownish or reddish color. (Plate ii.) 



