THE MIDDLE DEVONIAN TRAVERSE GROUP OF ROCKS 

 IN MICHIGAN, A SUMMARY OF EXISTING KNOWL- 

 EDGE 



By Erwin R. Pohl 



Of the Department of Geology, Vanderhilt University, NasJiville, Tenn. 



INTRODUCTION 



It has become more and more obvious with the progress of labo- 

 ratory and field studies on the faunas and stratigraphy of the Michi- 

 gan Traverse group of Middle Devonian age that no exact correla- 

 tion between deposits in the eastern and western parts of the State 

 can be established. This conclusion will serve as the focus of major 

 inferential consideration for the discussion that follows, and while 

 the greater portion of this paper will be devoted to the establishment 

 of the stratigraphic sequence of the Traverse Bay area, the truth of 

 the deduction will appear through comparison of this section with 

 the more completely developed group bordering Lake Huron. 



Newly introduced terms must necessarily be provisional, for the 

 study of this problem in its true light is still in its beginning. Such 

 names are here used merely as a means of clarifying a visualization 

 of the stratigraphic conditions contemporaneous with the deposition. 



From the standpoint of pure science the most engrossing phase of 

 geological investigation is to the author the derivation of faunas. 

 Marine faunas, so typically encountered in the Traverse, require 

 rational consideration. It appears trite to remark that an associa- 

 tion of shallow water invertebrate species, however long extinct, 

 reacted no more peculiarly to their environment than their livingj 

 representatives. It was an odd individual, not to say species or 

 assemblage, that would walk on dry land or fly through the air from 

 one basin of deposition to another. And yet, were we to allow the 

 gross differences in so-called conspecific forms and associations con- 

 sidered as being present contemporaneously in one and the same depo- 

 sitional basin to be disregarded — as they so flagrantly have been and 

 still are — we must accept some such supernatural attribute on the part 

 of formerly existing organisms. The pathway of encroachment by 

 the Traverse stages into Michigan vvill be studied by means of specie; 

 having characteristics limited by physical possibility. 



No. 2811.— Proceedings U. S. National Museum, Vol. 76, Art. 14 



G1590— 29 1 1 



