22 UNIVERSITY OF MISSOURI STUDIES 



mite, and the hollows are filled with a bluish, shaly dolomite. 

 The surface of many of the beds is covered with fucoidal mark- 

 ings, or is very rough, due to a nodular structure. One bed, 

 about 38 or 40 feet from the top, Is dense and hard, and rings 

 sharp when struck with a hammer. It contains small irregular 

 masses of quartz. This bed is persistent, having been seen in 

 several parts of the area. The pink, porous dolomite at the top 

 of the Elvins formation shows splendid cross-bedding (PI. V, 

 A), indicating very shallow water conditions at the close of the 

 period. 



No fossils were found in the upper part of the formation. 



The weathering of the beds produces a reddish mantle rock 

 where it is thick enough not to be affected by the organic acids 

 from the surface. It is usually very thin, and the underlying 

 rock is often exposed. The dolomite weathers out into small 

 rectangular fragments where thin-bedded, and into large rounded 

 boulders where massive. 



The following composite analysis shows the composition of 

 the Elvins dolomites : 



SiOj 6.20 



AI2O3 1.10 



FeO r ^^ 



MgO ' 20.01 



CaO 28.70 



COj 42.77 



H^O 42 



100.07 



Age and Correlation. — The age of the Elvins formation is 

 unquestionably Upper Cambrian. Only a few fossils were found 

 and they were brachiopods and cystoid stems. The latter were 

 very abundant in some of the lower beds. The brachiopods were 

 identified by Mr. D. K. Greger of the department of geology at 

 the University of Missouri, and the following species were 

 found: Eoorthis remnicha texana, Obolus matinalis, Lingulella 

 similia, and Obolus ismene? These fossils are regarded as Up- 

 per Cambrian in age. 



