27G THE DEVONIAN OF MISSOURI. 



DEVONIAN OUTLIER NEAR ROLLA, PHELPS COUNTY. 



The recent discovery of an outlier of Devonian near the 

 crest of the Ozark uplift has added new and important data on 

 the geologic history of the Ozark region. It indicates that the 

 Devonian seas extended to a much greater distance over the 

 uplift than has formerly been suspected. The following con- 

 densed description is taken from the Journal of Geology. 1 



Location and General Description. — The Devonian outlier 

 lies about 1 Yl miles northwest of Rolla, in the N. E. 34 N. W. 

 Y± Sec. 3, T. 37 N., R. 8 W. It is on the east side of the road and 

 lies fifty feet below the crest of the ridge. It occupies a little 

 knoll between two gullies, and when first found consisted of a 

 number of knobs of quartzite projecting from the hill and having 

 a rough alignment. The base was concealed, but just above the 

 top of the outlier were a number of Mississippian boulders, and 

 on the north, west and south at higher and lower levels are out- 

 crops of the Jefferson City formation. 



The summit of the ridge is capped by a thin stratum of 

 Pennsylvanian sandstone, and boulders of Pennsylvanian float 

 are found in abundance at lower levels. The Pennsylvanian 

 rests unconformably upon the Jefferson City formation on the 

 east side of the hill. On the west side there appears to be a thin 

 stratum of Mississippian between them, but the exposures are 

 very poor, and the exact relationships are difficult to determine. 



An excavation was made along the side of these quartzite 

 masses in an attempt to expose the lower contact. This was 

 not entirely successful, but the excavation showed that there 

 was a continuous ledge of quartzite at least thirty feet long and 

 from three to six feet in thickness, increasing in thickness toward 

 the east. Beyond the limits of the excavation there are a few 

 other knobs of quartzite, probably continuous with the part 

 just described. This makes the total length of the outlier about 

 fifty feet, and its greatest width slightly less. 



Litholoqic Characteristics. — Lithologically the Devonian rock 

 is a hard, dense quartzite breaking with a splintery fracture. 

 In color it ranges from white through gray to bluish and almost 

 black. The lighter shades predominate. Thin sections show 



>Bridge, Josiah. and Charles, B. E. A Devonian outlier near the crest of the Ozark 

 uplift, Jnl. Cieol. XXX, p 450-458 





