466 C. W. HAYES — COOSA VALLEY IN GEORGIA AND ALABAMA. 



before the Society again; also recent work by Mr Walcott on the 

 paleontology of the region has made possible certain stratigraphic cor- 

 relations of considerable interest. 



Physiography of the Region. 



The accompanying map shows the areal distribution of the formations 

 within the region, and the form of the surface is in large measure de- 

 pendent on the character of the underlying rocks. From Rome, shown 

 on the northeastern corner of the map, a line of hills extends diagonally 

 across toward the southwestern corner, culminating in Weisner moun- 

 tain. This line of hills separates the region into distinct physiographic 

 divisions. On the northwest is the Coosa valley, underlain for the most 

 part by soft shales and limestones which have been eroded down to a 

 nearly perfect plain. The level surface is interrupted by a few slight 

 elevations composed of harder shales or protected by a cap of coarse 

 gravel. The Coosa river has an extremely sinuous course, evidently in- 

 herited from conditions differing slightly from those which prevail at 

 present. Its channel is sunk 40 to 60 feet below the general level of the 

 valley, and its flood-plain has only a very moderate width. 



The southeastern portion of the area represented by the map is under- 

 lain by rocks of diverse character, and hence it has a more diversified 

 topography. Adjacent to the dividing line of hills above mentioned is a 

 narrow valley underlain by shales. South of Rome several other narrow 

 valleys diverge from tlijs one and penetrate a few miles within the border 

 of tlie high rolling land to the eastward. Between Cave spring and 

 Weisner mountain numerous narrow valleys alternate with irregular 

 ridges and hills. The dominant topographic feature of this region is 

 Indian mountain. It consists of several irregular ridges which coalesce 

 to form its highest point and taper off rapidly toward the northeast and 

 southwest. 



Stratigraphy of the Region. 



A detailed account of the lithologic character and distribution of the 

 formations of this region will shortly be published with the Rome and 

 Fort Payne atlas sheets, and only such details are included in the present 

 paper as are essential for an understanding of the stratigraphic and 

 structural problems. 



Cambrian Rocks. — Passing diagonally across the mapped area, from 

 Rome to Weisner mountain, along the northern base of the hills above 

 mentioned, is the intersection of a major thrust-fault plane with the land 

 surface. This has been named the Coosa fault on account of its relation 



