REVIEWS 



The Geology of Hardin County and the Adjoining Part of Pope 

 County. By Stuart Weller with the collaboration of 

 Charles Butts, L. W. Currier, and R. D. Salisbury. 

 Illinois Geological Survey, Bull. No. 41, 1920. Pp. 377, 

 pis. II, figs. 27. 



This report represents the results of three seasons' field work by the 

 author in conjunction with Messrs. Butts and Lee of the U.S. Geological 

 Survey and part of two seasons by Mr. Currier in the study of the fluor- 

 spar deposits of the county. In addition a chapter on the geography 

 of the region is contributed by Mr. Salisbury. 



Hardin County lies in the southeastern part of the state and wholly 

 within the Ozark country, an area of considerable relief and in a mature 

 stage of dissection. The history of the topography involves four periods 

 of uplift, the three cycles of erosion other than the present one, being 

 known as the Karber's Ridge, McFarlan, and Elizabethtown cycles. 



Structurally the area is characterized by rather flat-lying strata 

 surrounding an area of doming and intense faulting. The faults are of 

 the normal type and form a network along the edges of the dome which 

 is roughly circular in outline. They originated through the collapse of 

 the dome. Likewise remarkable is the presence within the region of 

 igneous intrusives in the form of dikes, sills, and plugs. The origin 

 of the dome involves the intrusion of these rocks, the collapse following 

 either the gradual spreading out of the lava or its partial withdrawal. 

 The structure is remarkable and has but few known parallels. 



The rock formations of the region include Devonian, Mississippian, 

 and Pennsylvanian sediments, involving a thickness of some 4,000 feet. 

 Of special note is the contribution to the knowledge of the Chester group. 



The oldest formation present, known locally as the Devonian lime- 

 stone, is correlated with the Lower Devonian, Onondaga, and Hamilton. 

 Lithologically it is a unit. The overlying Chattanooga shale contains 

 but a meager fauna and from its stratigraphic relation may be corre- 

 lated with either the Upper Devonian or Lower Mississippian, or both. 



The Meramec group, as originally defined by Ulrich, included the 

 Warsaw, Spergen, and St. Louis limestones. A study of the Ste. Gene- 

 vieve faunas convinces Professor Weller that this formation is much 



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