ARCELEAN GROUP. 257 



less marked than that of the folds alluded to; and it is also true that some 

 such structure seems necessary, as Dr. Dana has remarked, to explain the 

 subsequent geologic history of an extended adjacent area.* The uplift at 

 the close of the succeeding Algonkian Era affords, however, a raison d'etre 

 of sufficient importance, it would seem, to account for much of this. In 

 treating of the " Interior Continental " region, Dana divides it into three 

 portions or basins, whose boundaries consist of continental midribs, which 

 have been marked out very early in geologic time. As to the line running 

 northward from near our area, he writes: 



What determined this strong boundary line or limit is not clear ; possibly some under- 

 ground Archaean feature. 



In order to settle this important question, and to get information bearing 

 upon the extent of the more recent mineral- bearing strata, the writer made a 

 trip to the Wichita Mountains in the Indian Territory, the results of which 

 will appear at the close of Part I of this report. 



For the purpose of avoiding deductions not justified by present knowledge, 

 the local name of Burnetan System is here proposed for these rocks, from the 

 occurrence of good exposures in Burnet County. Although they correspond 

 lithologically and in other important particulars with the Laurentian System 

 of North America and Europe, it is not wise to attempt any close correlation 

 with distant outcrops until some more definite principles of classification are 

 established for the Archaean Group. There seems, however, to be abundant 

 reason for dignifying the strata with a more comprehensive title than that of 

 a series designation, both on account of the great unconformity succeeding 

 this period and the wide variety of the beds included. Then, too, the possi- 

 bility of epochal movements of importance lends color to theoretical divisions 

 of serial value. 



The visible portion of the Burnetan strata comprises areas of three more or 

 less distinctive classes, viz. : 



(1) The nucleal plateaus, presumably never covered by the sea since emer- 

 gence in the Archaean Era. 



(2) A series of irregularly concentric peaks, now bare, but perhaps once 

 covered by the later sediments. 



(3) Outlying peaks and portions of the escarpment surrounding the nucleal 

 plateaus, now capped by remnants of Paleozoic strata. These are of very 

 doubtful occurrence, certainly very rare. 



(1.) THE NUCLEAL PLATEAU REGION. 



It would require too much space to give all the evidence upon which the 



*Areas of Continental Progress in North America, and the Influence of the Conditions of 

 these Areas on the Work Carried Forward in Them. By Prof. James D. Dana, Bulletin 

 Geological Society of America, vol, I, 1890, p. 41, 



