32 GEOLOGICAL FORMATIONS 



( 4 ) Horizontal position of the stratified rocks on the 

 uneven and manifestly eroded surface of the crystallines. 



CAMBRIAN. 



Ozark Series. 



As already stated, the geological age of the Paleozoic 

 formations of Missouri, from the top of the column down as 

 far as the base of the Trenton limestone, has been deter- 

 mined satisfactorily. Below the calcareous division last men- 

 tioned is a great thickness of dolomitic limestones, with inter- 

 calated sandstone beds. They form what is commonly known 

 as the " Magnesian Limestone" series. The lithological char- 

 acters are very different from those of any of the later calca- 

 reous beds. Heretofore fossils have not been found abundantly 

 in this formation ; yet recent observations have indicated that 

 extensive faunas will be disclosed before long in the rocks 

 under consideration. 



Although it has long been known that the Magnesian lime- 

 stones are older than the Trenton, and that they lie immedi- 

 ately upon and against the Archaean crystallines uncomforma- 

 bly, their exact geological age has always remained unsettled. 

 There seems to be but little doubt, however, that part of 

 the series is equivalent to the Calciferous of other regions. It 

 is also pretty well determined that certain of the lower beds, 

 all below the " Saccharoidal " sandstone perhaps, are repre- 

 sentatives of the upper Cambrian or Potsdam. These conclu- 

 sions appear well grounded both upon stratigraphical and 

 faunal evidence. The rocks of the Ozark region have not as yet 

 received the necessary detailed study to enable the several 

 lines of demarkation to be drawn with certainty. Tbis inves- 

 tigation is now being carried on as rapidly as possible, and 

 promises very satisfactory and interesting results in the near 

 future. 



The early geological reports represent the Magnesian 

 limestone series as made up of seven members. Following 

 Swallow, these may be briefly described in the present con- 

 nection. Beginning at the top, they are: 



