110 PROCEEDINGS OF WASHINGTON MEETING. 



the Ozark uplift.* This dome-like protrusion is exhibited over an area of not 

 less than 15,000 square miles in the central portion of the state, south of the Mis- 

 souri river. Its location is represented in a general way on the small map form- 

 ing figure 25 by the broad white space west of the Iron [Mountain railway. It in- 

 cludes topographically the most elevated portion of the state, the plateau mass 

 called the Ozark mountains being within its bounds. The geological formations 

 represented are chiefly the Lower Silurian ; these occupying the whole central area 

 as massive sheets of magnesian limestone, with intercalated sandstones. Near the 

 center they lie generally in a nearly horizontal position, but toward the margin 

 of the uplift they slope off radially under the overlying formations. 



Age of the Upheaval. 



This upheaval was, apparently, thought by Broadhead t to have begun just before 

 the close of the earlier ( larboniferous, and to have continued until after this period. 

 The evidence of this would seem, however, far from conclusive. It consists in the 

 existence of outlying patches of lower Carboniferous rocks within the area of the 

 uplift and beyond the margin of the main body of the formation. These outliers 

 are not abundant, ami the most remote mentioned by Broadhead is an occurrence 

 of Chouteau rocks in Wright county, not over thirty miles from the margin of the 

 lower Carboniferous area- During the past field season discoveries of lower Car- 

 boniferous fossils farther in the interior have been made by Mr. .1. I>. Robertson, 

 assistant of the Missouri geological survey. They were found a few miles southeast 

 of Rolla, in Phelps county, and also near the northeastern corner of Douglas county. 

 The fossils were in a few loose fragments of chert scattered over the surface; no 

 rock being found in situ carrying such organic remains. These occurrences would 

 seem to indicate the former presence of the earlier Carboniferous sea over these 

 localities, or the submergence of the area, at that time. On the other hand, how- 

 ever, the scarcity of these Carboniferous rocks and the total absence of rocks 

 intervening between these and the Lower Silurian beds, within the main area of 

 the uplift, goes, so far as negative evidence can go, to prove that the intervening 

 beds were never deposited entirely over it; that the lower Carboniferous beds 

 reached up on its sides perhaps no farther than the limits of the outliers referred 

 to would indicate ; and that these latter, over the < >zark area, were of very limited 

 thickness, such as were subsequently readily removed by erosion. The last condi- 

 tion is in harmony with the hypothesis that these lower Carboniferous beds of the 

 ( >zark region were deposited during the earlier part of that period, and that their 

 accumulation was arrested by the emergence of the area during early Carboniferous 

 time while the upper beds were still in process of formation in surrounding zones. 



( )f movement and extensive uprising after the deposition of the lower Carbonifer- 

 ous rocks we have abundant evidence. This is shown by the unconformity which 

 exists between the lower Carboniferous limestones and the overlying Coal Measure 

 rocks. This unconformity has been so often described by Swallow,; Shumard,^ 

 Broadhead, || White,*! an ' 1 others as to call for no special demonstration or reference 



*The Geological History of the Ozark Uplift, by G. C. Broadhead: American Geologist, vol. vii. 

 1889, pp. 6-13. 

 I- Op. eit.,p.l2. 



J Report Mo. Geol. Survey, 1855. 

 Report Mo. Geol. Survey, 1871. 

 (Report Mo. Geol. Survey, 1873 and L874. 

 Tj Report Iowa Geol. Survey, 1867. 



