THE HISTORY OF DEVILS LAKE, WISCONSIN 353 



less than that of the present surface, and Devils Lake gap could 

 not have existed at the time. 



The exact age of this erosion surface is still an open question. 

 Where the plain and the gravel associated with it are known outside 

 this district, they have been assigned by different writers to differ- 

 ent ages. Winchell 1 long ago correlated these gravels in Minne- 

 sota tentatively with the Cretaceous, and following his lead Bain, 2 

 Calvin, 3 Grant and Burchard, 4 Hershey, 5 and others have con- 

 sidered the plain to have been formed chiefly during the Cretaceous 

 period. This correlation is, however, somewhat doubtful, for the 

 reason that it has never been proved that the gravel on the plain 

 in Minnesota is of Cretaceous age. It seems to lie on the Cre- 

 taceous, a relationship which tends to show that the plain cuts 

 across the edges of the eroded Cretaceous rocks and is therefore 

 post-Cretaceous in age, just as the fact that it cuts across the 

 Paleozoic sediments proves that it is younger than those sediments. 

 Most likely the plain is of Tertiary age. The evidence of this has 

 been presented by Salisbury 6 in an article in which he suggests the 

 correlation of these patches of gravel with the Lafayette formation 

 farther south. 



It is at least clear that the Devils Lake gap remained filled with 

 Paleozoic sediments while this plain was being formed, and that 

 the time involved was long. 



There are strong suggestions of a second flattish erosion surface 

 with remnants at about 1,200 feet. Representatives of this 

 surface may be found (1) cutting across the beveled edges of the 

 vertical quartzite beds of the North Range at the Upper Narrows, 

 (2) at the Lower Narrows, (3) 2 miles northeast of Denzer, (4) on 

 the summit of Old Flat Top, 1 mile southeast of the Lower Nar- 

 rows, (5) on the top of Gibraltar Rock, 1^- miles west of Okee, and 

 (6) forming saddles or low divides in the South Range, as on the 



1 N. H. Winchell, Geol. and Nat. Hist. Surv. Minn., I, 309-31, 353-56. 



2 H. F. Bain, Bull. U.S. Geol. Surv., No. 294, pp. 11-16. 



3 Samuel Calvin, Iowa Geol. Surv., IV, 43. 



4 Grant and Burchard, Lancaster Mineral Point Folio, U.S. Geol. Surv., p. 2. 



5 O. H. Hershey, Am. Geol., XX, 246-59. 



6 R. D. Salisbury, Jour. Geol., Ill, 655-67. 



