GENERAL STRUCTURE. 



37 



It has been intimated that there is probably a well-marked 

 physical break in the Magnesian limestone series at the top of 

 the "Second limestone." The present indications point strongly 

 to the supposition that the calcareous members of the series 

 below the line mentioned practically form one great limestone 

 formation, with numerous intercalated lens-shaped beds of 

 sandstone, arranged largely perhaps as already explained. 



For the entire Magnesian series — embracing the seven 

 numbers of Swallow — Broadhead* has recently given the name 



Ozark. 



If in future it seems advisable to separate the First Lime- 

 stone and Sandstone from the underlying strata, Broadhead's 



Fig. 2, Deposition of Ozark Rocks. 



name by slight restrictions may still be retained to designate 

 these rocks. 



It appears quite probable that the " First Magnesian " lime- 

 stone is the representative of the "Lower Magnesian" of the 

 upper Mississippi region, the Saint Peter sandstone being ab- 

 sent in Missouri, or rather represented by calcareous deposits. 

 As intimated previously, there seems to be considerable evi- 

 dence pointing toward a line of unconformity between the 

 Magnesian limestones below the " Saccharoidal " sandstone 

 and that rock. This horizon below the Trenton would appear 

 to be equivalent to the Chazy or upper Oalciferous of the Ap- 

 palachian districts. It may be regarded as made up of ( 1 ) a 

 more or less interrupted sandstone forming the basal and mar- 

 ginal portion; and (2) a magnesian limestone having a very 

 considerable geographic extent. 



« Am. Geologist, Vol. VIII, p. 83. Minneapolis, 1891. 



