AET. 14 MICHIGAN TRAVERSE GROUP POHL 33 



miles farther west. A study of the succession in the region of East 

 Bethany places the age of the two beds named as early Moscow. It 

 is unnecessary here to give a complete faunal list of those species 

 common to the portions of the sequence in Ontario and New York 

 under discussion, for these have been endlessly published elsewhere 

 without results. Suffice it to say that every species found at the one 

 locality may be identified at the other, even to the rarer forms, such 

 as Pugnax kernahani Whiteaves and Eleutherocrinus cassedayi 

 Shumard and Yandell. 



The westward migration by overlap of this portion of Hamilton 

 deposits into Ontario sharply delimits the upper boundary of the 

 Thunder Bay. The conditions of contact indicate a break of con- 

 siderable duress, and paleogeographical conditions in the upper 

 Mississippi Basin point to a comparatively early cessation of Trav- 

 erse sedimentation at this location. It is highly probable that Lud- 

 lowville and even Skaneateles time are represented here only by 

 the unconformity. This is necessarily so, for it has been shown 

 that the seas of the Traverse were slowly receding to the northward 

 shortly after their first encroachment in Presque Isle time. 



The stratigraphic position occupied by the Traverse group is thus 

 clearly delimited, as occurring between the Onondaga and the Ham- 

 ilton, and the time scale is extended by the interpolation of at least 

 700 feet of interrupted limestone deposition. 



DERIVATION. WHENCE CAME THE TRAVERSE? 



Throughout much of Paleozoic time invasion of North America 

 by epicontinental seas with northern connections was active. Axes 

 and basins had long been moulded in semipermanent trend, and their 

 positions were closely related to the derivation and distribution of 

 mid-Devonian strata in the northern Mississippi Basin. The meth- 

 ods by which paleogeographic conditions are reconstructed are essen- 

 tially paleontologic, for due to subsequent erosion or burial under 

 later deposits a case where it is possible to trace the overlap of beds 

 upon the barriers is exceptional. To reconstruct the geographic con- 

 ditions during the deposition of the Traverse beds we may fortu- 

 nately combine the physical and faunal criteria. 



Certainly the Traverse faunas have no close relatives in strata 

 having known southern connections. The Traverse stages are fur- 

 thermore paleontologically isolated from even the Middle Devonian 

 formations which were deposited in the same general region, which 

 in the case of the Hamilton beds overlap the former. Precise infor- 

 mation bearing on Middle Devonian remains found in the Arctic 

 and the northern Canadian Provinces is lacking and specific lists 



