GEOGKAPHIC SUBDIVISIONS 345 



they can be followed for 15 miles with but little change in textural or 

 mineral characters. 



West of Sturgeon lake the schists have become more hornblendic. 

 The attitude is notably changed from a gently southward dipping series 

 to one nearly vertical or northwardly inclined. Beds of limestone are 

 associated with the hornblende schists. 



Along the Kettle and Rum rivers still other conditions are seen. The 

 schists are markedly biotitic and of a much coarser texture than in the 

 Blackhoof and Kettle River valleys. Dikes of diabase occur and granitic 

 dikes and bosses constitute the larger proportion of the visible exposures. 



Reaching the Mississippi river from Haven northward for not less 

 than 30 miles, only granites of the hornblende-biotite type, occasionally 

 broken by diabase dikes and bosses of biotitic gabbro, are seen in so 

 many exposures that the conviction is forced that they constitute the 

 principal rock of the region. 



Finally, in another district with Little Falls as a center lies a series of 

 schists of somewhat diverse lithologic type, always regarded as the west- 

 ward extension of the Thomson slates. These have many characters — 

 mineral, chemical, textural, and structural — in common with those. 

 Around Thomson the clastic character of the series is clearly seen. 

 Here alteration has proceeded so far that no traces of a granular char- 

 acter have been noted — a condition explained by the proximity of 

 eruptive granites, gabbros, and diabases within the Little Falls district 

 (see map, plate 29). 



Rock Relations along the Border 



It has already been stated that at Short Line park, within the city 

 limits of Duluth, a well-boring discloses the Saint Louis River slates 

 beneath the Keweenawan eruptives, thereby establishing the northeast- 

 ward continuance of the series. In this locality there is no doubt that 

 the schists extend beneath the Keweenawan eruptives and elastics. In 

 the southerly part of Kimberly township, central Aitkin county, an ex- 

 posure of quartzite is reported, which, having the lithologic characters 

 of the more northerly Animikie, is on that ground relegated to that 

 later series.^ At Brainerd, in 1900, a well was bored by the Northern 

 Pacific railway. At 163 feet schists were struck of the general habit of 

 those northwest of Little Falls, and are presumably the same. 



Around the western end of the district there is no opportunity what- 

 ever afforded for determining stratigraphic relationships beyond the drift 



* Warren Upham : Preliminary report of field-work, Twenty-second Ann. Rept. Geological and 

 Natural History Survey of Minnesota, 1894, p. 28. (" Taconic series" is the term used.) 



