480 



E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



mouth of Illinois Eiver/^ 

 probably pinches out or be- 

 comes unrecognizable in the 

 vicinity of Hannibal, Mis- 

 souri. The facts in hand are 

 explained as follows: 



1. The whole series repre- 

 sents uninterrupted deposi- 

 tion in and adjacent to an 

 advancing shallow sea. 



2. The Everton, with its 

 basal layer of sand^ represents 

 deposition in embayments 

 while the sea was still con- 

 fined to areas south of Mis- 

 souri. 



3. The St. Peter sandstone 

 is a well developed beach 

 formed of wind-transported 

 quartz grains from the north. 



4. In the early part of ihU 

 stage the beach seems to have 

 gained on and possibly over- 

 come the advance of the sea 

 in northern Arkansas, but 

 subsequently it was itself 

 progressively drowned and 

 its development pushed north- 

 ward to some line beyond the 

 present limits of the St. 

 Peter. 



5. Finally, the Joachim 

 represents off-shore deposi- 

 tion during the latter half of 

 the time consumed in the tan- 

 gential deposition of the St. 

 Peter beach sands. 



^^ Apparently this is the formation to which the name Folly limestone was applied by 

 C. R. Keyes (Proc. Iowa Acad. Sci., vol. v, 1898, p. 61). 



