170 GENEKAX GEOLOGY. 



thickness, intercalated between layers of the quartzite. The 

 formation was originally an accumulation of sand with a 

 layer of clay, and the same metamorphic action which 

 changed the sand to a quartzite also converted the clay into 

 pipe-stone. The pipe-stone, containing a considerable amount 

 of per-oxide of iron, has a red color similar to, that of the 

 quartzite which encloses it. 



At New Ulm, in the valley of Minnesota river, other large 

 exposures of the same formation are found. This is the 

 most easterly point at which it has yet been recognized. It 

 appears only at the northern side of the valley there, having 

 a strong dip to the eastward, and an estimated thickness of 

 strata, that are more or less exposed, amounting to near four 

 hundred feet. A large portion of one of the exposures here 

 has the character of pudding-stone or coarse conglomerate. 

 It is also frequently exposed in Dakota Territory, west of the 

 Big Sioux river, where also some portions of it are in the 

 condition of metamorphic conglomerate. 



These exposures beyond the limits of the State are referred 

 to for the purpose of giving a fuller description of the forma- 

 tion than could be made from those within it, and for the 

 purpose of pointing out the original localities of those red 

 quartzite boulders that are so profusely scattered in the drift 

 of western Iowa. 



Economic Value. In a few rare cases this rock may be 

 quarried readily, as the layers are easily separated, but 

 usually it is so compact throughout that it is quarried with 

 the greatest difficulty into any forms except those into which 

 it naturally cracks. It has a great tendency, however, upon its 

 natural exposures, to break up by vertical fissures and cracks 

 into angular blocks of convenient size for handling. Except 

 this tendency to crack into angular pieces, which is not very 

 great in those already reduced to proper size for building 

 purposes, the rock is absolutely indestructible. The process 

 of metamorphism has been so complete that the rock is 

 almost everywhere of uniform texture, and the smoothness of 

 its fracture is sometimes such that mortar, unless the lime it 



