395 



The red argillaceous portion of the Primal series Prof. Rogers 

 regarded as having its counterpart in the remarkable mass of red 

 argillaceous shales and conglomerates occupying part of the south- 

 ern shore of Lake Superior. lie thought that the occurrence of 

 rocks thus characterized, in direct association with the Potsdam 

 sandstone, in regions where the stratigraphical relations are un- 

 equivocal, was a confirmation of the generally accepted opinion as 

 to the age of the Lake Superior cupriferous shales. In the pres- 

 ence of this fact, the argument for the Triassic age of these shales, 

 from their texture and color, is entirely valueless. Neither does 

 their cupriferous character furnish evidence, as has been supposed, 

 of their Triassic relationship. Throughout a great extent of the 

 Blue Ridge chain in Virginia, and its prolongation toward the 

 southwest, metallic copper and its ores are of very common occur- 

 rence, within and contiguous to the basement rocks of the Paleo- 

 zoic series. Referring to the systematic tracing of the rocks in 

 question by Foster and Whitney, by Owen, and by the Canadian 

 geolo";ists and others, and considering; the clear evidence afforded 

 bj the continuity of the deposits as well as the presence at dif- 

 ferent points of characteristic fossils. Prof. Rogers could see 

 no reason for questioning the conclusion now almost univer- 

 sally accepted by American geologists, that the Lake Superior 

 sandstones and shales belong to the lowest of the paleozoic de- 

 posits. 



In thus maintaining, in common with nearly all American 

 geologists, that this Primal group of rocks forms the lowest 

 member of the Paleozoic series in the United States, — the 

 lowest group in w^hich any traces of organic life have been dis- 

 covered, — Prof. Rogers would not be understood as asserting 

 that, in some yet unexplored part of the continent, a still low^er 

 group may not be found conformably beneath it. As, however, 

 the extensive explorations along its outcrop in the Appalachian 

 belt, the Canadas, and the Upper Mississippi, and observations 

 in the Rocky Mountains and elsewhere, have shown the Primal 

 group, even where most developed, to be limited to a few thou- 

 sand feet of strata resting discordantly on the so-called Azoic 

 rocks, it would seem highly improbable that any great down- 

 ward extension of our Paleozoic series will hereafter be brought 

 to light. 



