1 74 THE GEOLOGY OF MINNESOTA. 



[Limestones. 



oxide on weathering. This change of color is, noticeable in the rock of the 

 river-bluffs wherever they were cut out before the last glacial epoch. The 

 layers there have endured the exposure of a much longer period than 

 in the river bluffs between Fort Snelling and Minneapolis, where the strata 

 have been cut by the falls since the last glaciation. The shaly portions in 

 particular, when closely mingled with the calcareous are so stained and 

 hardened that the rock seems almost another formation. It becomes sep- 

 arated into layers of two or three inches, which have a dirty yellow color. 

 The quarries near Minneapolis, situated near the Ahoka county line, exhibit 

 this condition perfectly. Some of the first large buildings erected in St. 

 Paul, were made largely or wholly from such iron-stained and weathered 

 parts of this formation, and, although- they do not present that uniformity 

 of color and appearance of solidity and strength that the dark blue stone 

 lately quarried gives to a building, the stone itself has withstood the climate 

 and storms of this latitude more successfully than later buildings con- 

 structed wholly of the blue stone. Toward the southern portion of the state 

 this changed condition is not so noticeable, indeed is not so possible. The 

 beds are more compact and calcareous, and have less protoxide of iron, and 

 the effect of the elements is more superficial. Hence, while this formation 

 as a building material at its northern outcrops at St. Paul and Minneapolis 

 is rather inferior, at its southern exposures it furnishes a dark blue stone of 

 excellent quality. Nothing can be more suitable for heavy walls, and espe- 

 cially for foundations below the water table, and for all Gothic structures, 

 than the blue limestone taken from it at Fountain or at Faribault. 



Some of the principal buildings made wholly of this stone in St. Paul 

 may be mentioned, viz., the walls of the United States custom house and 

 post office are of this stone, the Catholic cathedral and the German Catholic 

 church are built wholly of it, also the Fire and Marine Insurance building, 

 the McQuillan block, Dawson's bank building, and many other business 

 blocks and several other churches, the St. Paul Roller mill, and the Wash- 

 ington and Franklin school-houses. 



At Mendota Gen. H. H. Sibley in 1836 built the first stone residence 

 in Minnesota. It is still in good condition. It is constructed of the 

 Trenton limestone, but shows the light yellow or buff color common to the 

 old stone buildings of St. Paul. The first stone structure in the state was 



