A. Window — Cambrian in Missouri. 223 



county on the west and corners witli Madison county on the 

 southwest. A description of the geology of this county by 

 B. F. Shumard was published in 1871,* from results of work 

 done during earlier years. According to this report the country- 

 lies on the eastern flank of the Ozark uplift and, proceeding 

 from the river westwards, the upturned edges of the eastward 

 dipping strata of Carboniferous, Devonian, Upper and Lower 

 Silurian ages are successively encountered. It is with the last 

 of these alone that we are concerned here. The report de- 

 scribes among the rocks of this period,f the First magnesian 

 limestone, the Saccharoidal sandstone, the Second magnesian 

 limestone, the Second magnesian sandstone and the Third 

 magnesian limestone, as they are found in this county, one 

 under the other, dipping gently to the east. 



The Second magnesian limestone, in which we are specially 

 interested, is stated to occupy a large area chiefly in the 

 central and northwestern portions of the county, and to ex- 

 tend across the eastern half of the county in a belt from one 

 to three miles wide. The Second sandstones, in which we are 

 also interested, is described as constituting the surface rock over 

 a larger portion of the country than any other formation and is 

 present in greater vertical development. It is particularly well 

 shown over the high central portion of the county. It is 

 described as varying in lithological character, but usually ap- 

 pears in thin beds of white, yellow, or reddish colors and made 

 up of moderately fine siliceous grains ; sometimes, however, 

 it is coarse-grained to the extent of being a grit-stone or con- 

 glomerate, containing large pebbles of milky translucent quartz. 

 The thickness is stated to be 150 ft. 



The Third magnesian limestone is described as occurring in 

 the western and southern portions of the county, with the 

 " usual lithological characteristics." 



Previous Results in Madison County. — The geology of 

 Madison county was described by Broadhead in 18734 Accord- 

 ing to this report the sedimentary strata till the valleys between 

 mountains and hills of Archaean rocks. The general section of 

 these strata given is as follows, from the top downwards. 



6. Sandstone. 



5. Chert beds and magnesian limestone. 



4. Magnesian limestone. 



3. Grit-stone with some magnesian limestone. 



2. Marble beds. 



1. Sandstone. 



* Report Missouri Geological Survey, 1871, pp. 289 to 303. 



+ Opus cit., pp. 298 and 299. 



% Report Mo. Geological Survey, 1873 to '74, pp. 342 to 379. 



