192 C. K. KEYES — A DEPOSITIONAL MEASURE OF UNCONFORMITY 



they consider as makino- up the Coal Measures of the state. Winslow's 

 section, however, is not without interest, and is giv^en below : 



Sebastian stage. 

 Spadra stage. 

 Norristown stage. 



Booneville stage. 

 Appleton stage. 

 Danville stage. 



Relations of Arkansan Series to great Unconformity 



correla tion 



From the foregoing it is seen that the Lower Carboniferous or Missis- 

 sippian series, with its minor divisions, is well defined in northern 

 Arkansas. The Kaskaskia terrane is easily identified, passing upward 

 south of the Boston ridjre into the Coal Measures. 



FiGi'KE y. — Rclntions oj Arknnsnn Scries {hlnrk) to the other Cnrboniferous Series. 



Tlie basal horizon of the lowest Coal Measures of Missouri, or Des 

 Moines series, is believed to extend southward, and to the south of" the 

 Arkansas river to coincide ap})roximately with the Grady coal horizon, 

 or the base of the Cavaniol. 



With the base of the Des Moines series of Missouri thus located in 

 Arkansas, and the top of the Lower Carboniferous well defined, it leaves 

 ^ in the south an immense thickness of nearly 18,000 feet of sediments 

 that are in the north wholl}^ unre[)res6nted by deposits. The 18,000 feet 

 of sediments were manifestly laid down during the period represented 

 by the stratigraphic break at the base of the northern Coal Measures. 



DEPOSITIONAL MEASURE OF EROSION PERIOD 



The magnitude of the hiatus at the base of the Coal Measures of Iowa, 

 Missouri, and Kansas is readily appreciated when we find a place where 



