HISTORICAL SKETCH. 5 



1850, Owen.] 



ous rocks on the sedimentary is prominently brought out in the report. 

 This complicates the geology and renders the identification of the rocks 

 both difficult and sometimes erroneous. In conclusion he remarks "that 

 there is perhaps no extinct volcanic region in the world where trap and 

 other igneous intrusions can be studied to better advantage than in the 

 country bordering on the northwest shore of lake Superior. Not only are the 

 vertical dykes numerous and conspicuous, but there are abundant examples 

 of overflows, as well as inter] aminated insinuations producing all degrees 

 of metamorphosis on the adjacent strata, graduating from mere indiu-ation 

 of the beds to complete obliteration of stratification and sedimentary origin, 

 so that the beds of deposition become confounded with the igneous masses 

 that have invaded them and produced such extraoi'dinary changes." 



Dr. B. F. Shumard made the only examination of the valley of the 

 Minnesota; which he ascended as far as the mouth of the Redwood river. 

 At that point he was attacked with pleurisy, and was compelled to return 

 hastily to Traverse des Sioux and Fort Snelling. His report exhibits 

 the first attempt ever made to parallelize the rocks of the valley 

 with those of the rest of the state, or to determine their age by 

 reference to a known standard of nomenclature. He recognized Dr. 

 Owen's Nos. 2C and 3A, at the mouth of the river in the Fort 

 Snelling bluff, i. e. the Trenton and Black River limestones, and the St. 

 Peter sandstone. At Shakopee, and thence to Little rapids (near Carver) 

 he notes the Lower Magnesian. The sandstone at the last place he regards 

 as belonging to a formation several hundred feet below the white sandstone 

 of the Fort Snelling bluff,* and probably to the sandstones of Formation 1. 

 The limestone and sandstone exposed at intervals from Shakopee to Man- 

 kato, forming the immediate bluffs of the river, and constituting several 

 islands, he refers to the Lower Magnesian and the sandstones of Formation 1. 

 Ascending the Blue Earth river six or eight miles, and observing the same 

 geological horizon as far as he went, he notes subsequently two or three 

 exposures of Formation 1, before reaching the mouth of the Waraju (Cot- 

 tonwood) river, one being two miles below the mouth of that stream. The 

 red quartzyte opposite the mouth of the Waraju he regards as the lower beds 



*It is the Jordan Sandstone, and lies about seventy-flve feet below the sandstone of the Fort Snelling bhiff, the Sha- 

 kopee limestone separating; them. 



