8t. Joseph and Potosi Limestones of Missouri. 361 



out exception a crystalline limestone, nearly, if not quite, pure. 

 Accompanying the conglomerate is an oolitic limestone. 



Although not traced continuously, to the points noted, the 

 conglomerate is assumed to be identical, for the following rea- 

 sons: The disk-like conglomerate, the crystalline limestone 

 paste, the oolitic limestone, and finally, the invariable occur- 

 rence of fossils, principally trilobites and brachiopods; also 

 beds of interstratified slate. 



Fossils are very scarce in rocks of both formations save as 

 here noted: Lingidella and Obolella in or near the junction 

 between the La Motte sandstone and the St. Joseph ; in the 

 bands of lead-bearing clay slate in the lower and upper lead- 

 bearing zones of the St. Joseph limestone (see geological column) 

 and in the slates of the conglomerate series ; in the conglom- 

 erate paste (trilobites, brachiopods, pteropods). 



The writer feels little hesitancy, therefore, in stating posi- 

 tively that the beds of conglomerate mark a break in geological 

 time between the St. Joseph and Potosi limestones. There is 

 no doubt that this division will be found to be widely extended, 

 but at present nothing can be here offered in support outside 

 of St. Francois county and the eastern edge of Iron county. 



The Potosi will henceforth be recognized as including and 

 lying above the slates and conglomerates, and will extend far 

 down many of the streams instead of being referred to the hill 

 tops above. 



As to the age, its determination rests on fossils, and these 

 have been submitted to Professor Beecher, who has generously 

 consented to examine them. 



