224 A. Winslow — Cambrian in Missouri. 



The members of this section numbered 1, 2, and 3 and part 

 of 4 are placed in the Potsdam ; the upper one hundred feet 

 or more of 4 are described as belonging to the Third magnesian 

 limestone ; numbers 5 and 6 are placed in the Calciferous 

 and b' is thought to be probably the "Third sandstone." 



The lowest sandstone (1) is described as occurring in the 

 northern part of the county, in between the granite hills ; it 

 is generally fine grained and of white or buff color, or may be 

 a coarse, brown or red conglomerate. Thicknesses of from 40 to 

 90 feet are exposed in places. The sandstone found about 

 Mine La Motte is included in this description. 



The marble beds (2) are found only at a few localities in the 

 central and southwestern portions of the county. The grit- 

 stones are similarly exposed only at a few points. The mag- 

 nesian limestones (4) are stated to be of wide distribution ; the 

 lower beds are placed in the Potsdam and are separated from 

 the upper beds, of 100 feet or more, which are grouped under 

 the head of the Third magnesian limestone, though the reasons 

 for this separation are not very clear. The chert and sand- 

 stones (5 and 6) occupy the hill tops in scattered patches. 



JSTo explanation is given of the stratigraphic structure of 

 county and the reasons for differentiating the marble and grit- 

 stone beds (2 and 3) and for placing them at the places desig- 

 nated in the section are not plain. 



Previous Results in St. Francois County. — No report 

 especially describing St. Francois county has been published ; 

 but the sedimentary rocks there are in direct continuation of 

 those of Madison county and the prevalent limestone has 

 generally been considered to belong, in great part at least, to 

 the Third magnesian. According to our understanding, then, 

 the interpretation of the stratigraphy and structure of this 

 region to be drawn from these reports would be as is expressed 

 in the following section, along the line A, B, drawn in the 

 sketch map on p. 222. 



A 



Fig. 2. — A generalized section across St. Francois and St. Genevieve counties, 

 expressing the results of early work. 



Eesults of the present Geological Survey. — During the past 

 few years the present Geological Survey has prosecuted field 

 work during part of each field season in this section of the 



