MAGNESIAN LIMESTONES 33 



First Magnesian limestone. 



First, or Saccharoidal, sandstone. 



Second Magnesian limestone. 



Second sandstone. 



Third Magnesian limestone. 



Third sandstone. 



Fourth limestone. 



The " Fourth " JMagnesian limiestone, or lowest number of 

 the Ozark series recognized, has its typical exposures along 

 the Niangua and Osage rivers in Morgan and Camden counties. 

 The basal grits, conglomerates and associated calcareous beds, 

 underlying the Third Magnesian limestone in the Iron Moun- 

 tain region, have been thought to be the shore representatives 

 of this limestone, in part, at least. Perhaps, also, further re- 

 search will reveal other strata below the lowest beds of the 

 Ozark now known. According to the measurements of Swal- 

 low, the " Fourth " Magnesian limestone has an exposed thick- 

 ness of more than 300 feet at the center of a broad anticline 

 on the Niangua river. 



Lithologicallyit is described as a buff, coarse-grained dolo- 

 mite, similar to the other magnesian strata of the series, but 

 with few cavities and very little chert. It is heavily bedded, 

 and along the streams where exposed forms high mural escarp- 

 ments and precipitous cliffs. 



Of the " Third " sandstone little has been said. It is doubt- 

 less merely a local occurrence. So far as is known it has only 

 been reported on the Niangua river in Camden county, where it 

 attains a thickness of about 30 feet. Broadhead thinks that 82 

 feet of this sandstone were passed through in drilling the deep 

 well at the Saint Louis County Insane Asylum. 



This sandstone is very massive, showing but little tendency, 

 in weathering, to emphasize the lines of stratification. In many 

 places, however, cross-bedding is well defined, indicating the 

 shallowness of the water at the time of deposition. Usually 

 the sandstone is very soft and incoherent, with little foreign 

 material intermingled. 



