CLASSIFICATION GRADATION AL AND LITHOLOGIC CRITERIA 479 



inces. Thus the Galena dolomite of the upper Mississippi Valley is not 

 of the same age as the pure crystalline Kimmswick limestone found to the 

 south of St. Louis, The Galena is younger. The Silurian dolomites of 

 Wisconsin and Iowa and the purer limestone of the same period in Ken- 

 tucky and western Tennessee also are most probably not strictly con- 

 temporaneous deposits. At least they belong to distinct provinces, within 

 which each series of formations maintains its lithic characteristics without 

 any sign of intergradation in the median areas. 



Some lateral change in lithology of possibly contemporaneous zones is 

 suggested by comparison of the Waverlyan deposits in Ohio and eastern 

 Kentucky, with the Fort Payne and TuUahoma formations in Alabama 

 and Tennessee and the Boone and Osage group of limestones in Arkansas, 

 Missouri, and Iowa. Also in comparing the Chesterian deposits in north 

 Arkansas with those in western Kentucky and Illinois. But even in these 

 two cases the exact contemporaneity of the local developments is only in 

 part true or probable, for at least some of the zones of the series or groups 

 in the several contrasted areas did not stretch unbrokenly from Ohio to 

 western Arkansas and Iowa in the first case and around the southeastern 

 flank of Ozarkia in the second. As for the other zones the several basins 

 were sufficiently distinct in features influencing sedimentation to develop 

 corresponding local peculiarities. (See further statements, pages 318, 

 425, 452, 582, 586 593.) 



The case of the St. Peter sandstone. — But there seems to be at least 

 one well marked case of landward change in character of deposit in the 

 Mississippi Valley, namely, the series of deposits of which the St. Peter 

 sandstone is the most important member. As shown in the accompanying 

 sketch, this series begins in the southern embayments of Ozarkia with a 

 thin basal sandstone or fine conglomerate resting unconformably on the 

 Yellville. This is followed without apparent break by from 1 to approxi- 

 inately 100 feet of fine grained, slightly magnesian bluish dove limestone, 

 to which the name Everton is applied. Locally the Everton is thickly 

 charged with floating rounded quartz grains; at other places it is almost 

 entirely free of sand. Usually its top grades rather rapidly into typical 

 St. Peter sandstone, and this in turn passes by gradual transition into the 

 overlying Joachim dolomite. 



Tracing the series northward in the Mississippi Valley it is found that 

 the Everton drops out before reaching the border of Missouri. Of the 

 succeeding members the St. Peter sandstone extends far into Minnesota 

 and "Wisconsin, but the Joachim, which, is still well developed at the 



