Application of principle of transgressive overlap 



Cambric. 

 Reagan Sandstone 



579 



Feet 



Calcareaus sandstones, thin bedded and laminated, grading downward 

 into clays and greensands, with coarser sands lower down, which 

 pass downward into quartzites and arkose conglomerates of poorly 

 assorted granitic material. At the top of the sandstone and in the 

 shaly and calcareous strata for several hundred feet above the 

 sandstone (basal part of Arbuckle), fossils of Middle Cambric age 

 occur. The thickness averages 300 feet, but varies from almost 

 nothing to 500 



Great unconformity, with irregular erosion surface. 



Granite and porphyry. 



The occurrence of Middle Cambric fossils in the Eeagan sandstone 

 marks the beginning of the time of sedimentation as Middle Cambric 

 and probably as the early portion of that period. There is, then, ar± 

 overlap from the southeast, where the basal sandstone and a considerable 

 part of the limestone is of Lower Cambric age. 



In the Ozark region the following section of the basal Paleozoic rocks 

 is exposed:* 



Feet Feet 



Joachim limestone to 150 



Crystal City sandstone to 200 



Jefferson City limestone 50 to 250 



Roubidoux formation 70 to 225+ 



Gasconade limestone 450 to 650 



Elvins formation to 120 



Bonneterre limestone 200 to 500 ? 



La Motte sandstone to 300 



Great unconformity. 



Archean granites and porphyry. 



The La Motte sandstone constitutes the basal formation of this section 

 and was formerly identified as Potsdam sandstone. It is frequently a 

 coarse grit or conglomerate near the base, the pebbles being quartz or 

 granite and porphyry, and in the Saint Francis Mountain region a con- 

 glomerate of porphyry pebbles lies at the base of the formation. Upward 

 the La Motte becomes more thinly bedded and flaggy, and calcareous 

 beds make their appearance, the transition to the overlying Bonneterre 

 being gradual. The sandstone may disappear altogether, probably along 



* Bain (H. Foster) and Ulrich (E. O.) : The copper deposits of Missouri. Bull. no. 

 267, U. S. Geological Survey. 



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