54 UNIVERSITY OF MISSOURI STUDIES 



of various shapes but are characteristically flattened, many of 

 them being one to two inches thick, eight to twelve inches long, 

 and four to six inches wide. All the chert occurs along definite 

 horizons. 



The sandstone beds vary from one inch to five feet in thick- 

 ness. Usually they are thin and inconspicuous. They consist of 

 well-rounded grains of quartz which are fine to medium-sized, 

 the whole being usually well stained with iron oxide. In places 

 they are well cemented; in other localities they are very friable. 

 They contain chert at many points, and cross-bedding is common 

 in them. The Jefferson City formation weathers to a red or 

 brownish-red soil which contains considerable chert on the slopes. 

 It is sufficiently deep over most of the outcrops of the Jefferson 

 City to form good agricultural land ; in fact, it is the best soil de- 

 rived from any of the formations in this area. 



The formation, as a whole, is horizontally bedded, although 

 it is locally slightly folded, a feature that is very common in all 

 the formations the writer has seen in Missouri. All these slight 

 undulations are small and are doubtless the result of unequal 

 shrinkage, aided by crystallization. 



The fact that these three formations are all conformable, 

 have similar characteristics, and grade into each other suggests 

 that they are in reality one formation, and that names have been 

 applied to members only. The present names and divisions are 

 inheritances from the work of Swallow, whose divisional lines 

 were purely lithological. From what the writer has seen of these 

 formations, they could all be included under one name, and then 

 would present more characters of unity than many other forma- 

 tions which have had their limits established through structural 

 and faunal evidence. Subdivision is to be desired, but there 

 should be reasonably definite lines of demarcation. 



There is a marked unconformity at the top of the Jefferson 

 City formation. The shallow-water sea in which it was deposit- 

 ed was changed to land which was eroded and then depressed 

 sufficiently to receive the St. Peter sandstone. 



Summary. — These formations indicate shallow seas. The 

 larger part of them is dolomite, but there is also much chert and 

 some sandstone. All three formations contain these several sorts 



