528 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



440 feet of shaly and massive Sycamore limestone, and this included mass 

 is bounded both above and below by an unconformity. Finally the hiatus 

 at the top of the Sycamore is regarded as representing the time during 

 which some 10,000 to 15,000 feet of Stanley shale and Jackfork sandstone 

 were deposited in the near-by Ouachita synclines. This opinion is based on 

 three facts: (1) that the S3^camore contains early Tennessean fossils; (2) 

 that the Stanley shale contains younger, probably early Pottsville plants, 

 and (3) that the typical Caney shale overlies the Jackfork sandstone. 



(7) Passage beds with or without interrupted sedimentation. — Tran- 

 sition from one kind of sedimentary rock to another — as from a sand- 

 stone to a shale or from either to a limestone, or from a limestone to a 

 shale — even when the change is abrupt, often occurred without discon- 

 tinuity of deposition. On the contrary, even a "gradual passage" does 

 not preclude the possibility of a long interruption of the process of sedi- 

 mentation at such places and times. 



Interruption in the latter cases is least likely when the transition is 

 from sandstone to shale deposition. Transition without break occurred 

 also, though rather infrequently when the passage is from shale, or even 

 from sandstone, to limestone. Theoretically such transition signifies 

 merely a lowering of the land with respect to sealevel, as when erosion of 

 the land reduces its gradient, so that the coarser clastic deposits give way 

 to finer-grained sediments, or when the sea rises higher and higher witli 

 respect to the land. 



Occurrences of transition from sandstone to shale and from shale to 

 limestone without known interruption of deposition are too common io 

 require citation of instances. Uninterrupted transition from sandstone 

 to limestone, not counting passages from such thin, sandy and con- 

 glomeratic, initial deposits of overlapping limestone formations, like the 

 Devonian limestone on the north flank of the Ozark uplift and certain 

 Kinderhookian limestones on the south flank of the same, in Missouri, 

 are less common. The passage from the Potsdam sandstone to the Little 

 Falls dolomite in New York, from Oriskany sandstone to Oriskany lime- 

 stone in Maryland, east of Hancock, and from the Jordan sandstone to 

 the Oneota dolomite in the upper Mississippi Valley, are fairly good 

 examples. An excellent and indubitable instance is seen in the tran- 

 sition from the Saint Peter sandstone to the Joachim magnesian lime- 

 stone in eastern Missouri and northern Arkansas. On casual inspection 

 the passage from the sandstone to the limestone, in especially the last 

 of these cases, may seem abrupt, but on close examination it is usually 

 found that the lower part of the limestone is filled with downwardly 

 multiplying, floating, and probably wind-blown grains of quartz. 



