66 THE GEOLOGY OF MINNESOTA. 



[Lea, 1836. 



The glazed or polished surface of the quartz rocks at the pipestone quarry, I consider a very 

 interesting subject, and one which will hereafter produce a variety of theories as to the manner in 

 which it has been formed and the causes which have led to such singular results. The quartz is 

 of a close grain and exceedingly hard, eliciting the most brilliant sparks from steel, and in most 

 places where it is exposed to the sun and air, its surface has a high polish, entirely beyond any 

 result which could have been produced by diluvial action, being perfectly glazed as if by ignition. 

 I was not sufficiently particular in my examination to ascertain whether any parts of the surface 

 of these rocks under the ground, and not exposed to the action of the air, were thus affected, 

 which would afford an important argument in forming a correct theory with regard to it ; and it 

 may also be a fact of similar importance that the polish does not extend over the whole wall or 

 area, but is distributed over it in sections, often disappearing suddenly and reappearing again, 

 even where the character and exposure of the rock are the same and unbroken. In general, the 

 points and parts most projecting and exposed, bear the highest polish ; which would naturally be 

 the case, whether it was produced by ignition or by the action of the air and sun. It would seem 

 almost an impossibility that the air in passing these projections for centuries, could have produced 

 so high a polish on so hard a substance, and, in the total absence of all igneous matter, it seems 

 equally unaccountable that this effect could have been produced by fire. I have broken off speci- 

 mens and brought them home, which have as high a polish and luster on the surface as a piece of 

 melted glass; and then as these rocks have certainly been formed where they now lie, it must be 

 admitted that this strange effect has been produced either by the action of the air or by igneous 

 influence, and if by the latter cause, we can come to no other conclusion than that these results are 

 volcanic ;* that this wall has once formed the side of an extinguished crater, and that the pipestone, 

 lying in horizontal strata, was formed by the lava which issued from it. I am strongly inclined to 

 believe, however, that the former supposition is the correct one, and that the pipestone, which dif- 

 fers from all known specimens of lava and steatite, will prove to be a subject of great interest, 

 and worthy of careful analysis. 



The first plate-page is designed to show at a glance the history of geo- 

 graphical exploration in Minnesota, from the time of the earliest French 

 exploration to the date of Catlin's visit to the pipestone quarry. Plate-page 

 No. 2 is a reduced copy of Franquelin's map of 1688, being the oldest known 

 map of the region west of lake Superior. 



LIEUT. ALBERT M. LEA ON THE BLACK HAWK PURCHASE. 



Lieut. A. M. Lea's map, accompanying his report on the "Black Hawk 

 purchase," entitled " Notes on the Iowa District of Wisconsin Territory," 

 1836, shows the southern and southeastern counties of Minnesota, and the 

 tributaries of the Mississippi river as far north as the foot of lake Pepin. 

 The Whitewater river, by this map, joins the Embarras river just before 

 the latter reaches the Mississippi. A tributary of the Whitewater from 

 the south is named Swallow creek. Lake Albert Lea is there styled Fox 

 lake. Fountain lake he styled Chapeau lake. A branch of the Blue Earth 

 river is represented, and Council lake as one of its tributaries. This is 

 probably Walnut lake, of Faribault county. The head of Lime creek is 



*Tliese smoothed surfaces are due to the polishinR effect of sand and dust driven by the high winds. N. II. W. 





