KELATIOX BETWEEN STRUCTURE AND CONFIGURATION. 



227 



directions of these dips varied rapidly. While slowly meander- 

 ing through the country on horseback, with only an occasional 

 extended view from some peak, each topographic feature pre- 

 sented itself separately, and the differences in size, in outline, in 

 profile and in trend, within comparatively small areas, added 

 to the confusion of conception. It soon became evident that 

 the problems which this country presented could be solved only 

 through detailed work in which delineation of the topography 

 must play an important part. Thus we came to the construc- 

 tion of the detailed topographic maps which are now being 

 engraved, and which will appear in a forthcoming report of 

 report of the Arkansas geological survey. 



The small topographic map accompanying this paper, plate 

 8, is condensed from these detailed maps. It expresses only 

 faintly, however, much that is shown to be of geological signifi- 

 cance on the large sheets. As the construction of these sheets 

 progressed, order began to develop itself; the relations of dis- 

 connected parts gradually became apparent; until now, as 

 completed, the maps themselves stand as the solutions of vari- 

 ous problems for the solving of which they were originally 

 intended to be only one of the mean. To some of the results 

 of this work I now wish to call attention. 



Age of the Rocks of Western Arkansas. 



From the time of Owen's work, preceding the year 1860, the 

 belief has been prevalent that the coal beds and associated rocks 

 of western Arkansas are of sub-conglomerate or lower Carbon- 

 iferous age. Without analyzing the reasons for this conclusion 

 here, it suffices to say that our present knowledge of the flora of 

 these coal beds, as well as the results of independent strati- 

 graphic studies, lead to the conclusion that the coal beds of the 

 Arkansas river and the associated rocks belong w-ell up in the 

 Carboniferous system. The complete display of the evidence 

 leading to this conclusion is reserved for a future publication, 

 since this question is not properly an essential part of this 

 paper ; but in general terms the line of argument is as follows : 

 In northw^estern Arkansas, in the vicinity of Fayetteville, Ar- 

 chimedes limestones and other rocks of probable lower Carbon- 

 iferous age are well developed. Thence southward, across the 

 Boston mountains, several cross-sections have been constructed 

 with the results of proving the existence of barren strata over 

 1,000 feet in thickness intervening between these limestones and 



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