398 * A. C. LANE 



At Marinette, too, the samples at 290 and 300 to 325 feet are 

 shaly, blue, pyritiferous, and a well near Maple Ridge shows that 

 this blue shaly base is persistent. Beneath it is a marked horizon 

 for water. In the Neebish well, the bluish shalier base is distinct 

 between 158 and 186 to 205 feet, but other correlations can hardly 

 be made. I do not believe that we can yet tell where to draw the 

 line between the Middle and Upper Ordovician on Grabau's latest 

 plan, his Chazyan, and Trentonian-Cincinnatian-Nashvillian, nor 

 divide into the epochs made by Schuchert, though possibly this blue 

 shale may mark the culmination of submergence, the beginning of 

 emergence. It is quite clear that the Trenton, as used in Michigan 

 and generall}- in the West, corresponds closely with Clarke and 

 Schuchert's Mohawkian, including whatever there may be of Chazy 

 and Stones River (Lowville or Birdseye), Black River, and Trenton. 



The section on the Escanaba River is said by Hall to be less than 

 75 feet (p. 144) and to include 15 feet near the top, gray, meagerly 

 fossiliferous (p. 146). Rominger estimated it at 100 feet. But a 

 close correlation of the various outcrops with well-sections has not 

 yet been made. Until it is, it seems to be conservative in the matter 

 of names. 



While Escanaba limestone, suggested by Grabau, is a euphonious 

 term, my impression is that it would be better to use Trenton, the 

 old widely used term, in a broad sense and introduce Escanaba as 

 applicable to some accurately defined subdivision. The triple division 

 above suggested might perhaps be improved for paleontological pur- 

 poses by transfer of a few feet. I think, however, that the occurrence 

 of a sandy middle member, and especially a blue shaly lower, will 

 be found widespread. 



The Trenton limestone marks the culmination of Ordovician 

 depression, when the land masses seem to have been fully buried 

 far and near, while at the same time conditions for animal life were 

 very favorable. As Limestone Mountain on Keweenaw Point shows 

 the Trenton extended much farther than shown on Chamberlin and 

 Salisbury's map (II, Fig. 129, Schuchert's map, 57 to 58). The 

 thickness of the whole Trenton, including the Galena, is best taken 

 from the Wagner wells (1903, p. 134) as 271 feet. The records do 

 not indicate that it thins much to the east. Oil wells in Manitoulin 



