of the Devonian of Western Tennessee. 733 



Acknowledgments. — The present study was begun in 

 1916, when the writer spent two months in the field, mak- 

 ing a large collection of fossils and gathering data which 

 formed the basis of a monograph presented in 1917 as a 

 dissertation for the degree of doctor of philosophy at 

 Yale University. The problem proved so fruitful of 

 results that, thanks to the interest of the late Doctor 

 A. H. Purdue of the Tennessee State Geological Survey, 

 the writer was enabled to spend two additional months in 

 the field during the summer of 1917, and to elaborate the 

 original study into a completed report. 



The original investigation was made possible by the 

 kindness of Professor Charles Schuchert of Yale Univer- 

 sity, and the preparation of the manuscript has been done 

 in the laboratories of the Peabody Museum under his 

 constant supervision. It is a pleasant duty to acknow- 

 ledge the writer's indebtedness to Professor Schuchert 

 for many helpful suggestions and criticisms. Thanks 

 are also due Doctor Bruce Wade for valuable informa- 

 tion given in the field, and for several collections of 

 fossils. 



Location. — The Devonian rocks of Tennessee are 

 exposed in numerous small irregular areas in a narrow 

 belt along the western valley of the Tennessee River. 

 They are best developed in Benton, Decatur, Perry, and 

 Hardin counties. With very minor exceptions, this 

 narrow belt across the state embraces all the Devonian 

 strata save the widespread Chattanooga shale. (See 

 map, fig. 1.) 



Steatigeaphy and Coeeelatiok 



Introduction. — The Devonian rocks in Tennessee suc- 

 ceed those of the Middle Silurian, the contact being a 

 disconformable one, usually with little physical evidence 

 to direct attention to the long interval which separates 

 these two series. In most of the exposed sections the 

 Lower Devonian rests on the massive Decatur limestone, 

 but in the more eastern occurrences it overlaps younger 

 Silurian formations. SafTord long ago recognized that 

 these Lower Devonian strata form a westward-thickening 

 wedge separating the Silurian limestones from the suc- 

 ceeding but much younger Mississippian shales and 

 chert, and that they pinch out and disappear within a few 

 miles east of the Tennessee River. 



