540 THE GEOLOGY OF MINNESOTA. 



[Pipes tone quarry. Quar!zyte. 



layer, and to have followed along its strike north and south nearly a mile, 

 without penetrating very deeply into the rock. The layer which furnishes 

 the pipestone is about eighteen inches thick, and is embi'aced between 

 heavy layers of the same rock as the ledge already described, and they all 

 dip together toward the east, and of course run under the main escarpment. 

 The present quarrying is a little east of the line of old diggings, but follows 

 along the strike of the formation the same as the other, the only difference 

 being in having greater depth (the pipestone layer is about six feet under 

 the ground here) arid in the difficulties encountered in removing about five 

 feet of very firm pinkish quartzyte in heavy beds. 



Southward from the region of the pipestone quarry the land continues high, and in some 

 instances there are ridges, or long knolls, of drift, that are broad and evenly rounded over by 

 a thin loam. The first exposure of the rock, in the vicinity of the road to Luverne, is on 

 section 13, Eden, along the outside of the valley that crosses westwardly near the center of the 

 section. It extends about a mile east and west. It here is seen to form an undulating floor on 

 which the loam is thinly spread. It is hard, massive, pinkish-colored and superficially vitrified, 

 in some places also showing two directions of glacial striae, one being by the true meridian S. 10 W., 

 and the other 8.42 E. 



The same line of rocky outcrop extends westwardly to the Split Rock creek, and along that 

 creek and its eastern tributaiies as far as it continues in the state. It seems to have a changeable 

 dip, but nowhere presents perpendicular bluffs. 



On the N. E. } of section 36, Eden, is another exposure of this quartzyte. It is along a 

 shallow ravine that makes westward. It is seen again on the high prairie about half a mile farther 

 south. 



At a point about ten miles north of Luverne this rock becomes frequently exposed both in 

 the valleys and on the hills, and continues so to the mound near Luverne, where it suddenly 

 breaks off, along the west side of Rock river, and is not known to the south of that place. 

 Throughout this distance it forms a high plateau three or four miles wide and about a hundred 

 feet higher than the prairies east or west, but the surface, though frequently rocky, is not rough. 

 It is undulating; and the plateau sinks gradually down to the level of the rest of the country on 

 either side. This plateau terminates abruptly in a rocky and precipitous bluff facing southeast- 

 ward, three miles north of Luverne, in what is known as "the mound." There is a very large 

 rocky outcrop in sections 4, 5, 6, 7 and 8, Mound. There are frequent exposures in Mound and 

 Spring Water townships. The Split Rock creek which crosses the northwest corner of Rock 

 county has frequent exposures both in Rock and Pipestone; but in Pipestone the rock range veers 

 toward the east, into the east part of Eden township, and disappears till reaching the region of 

 the pipestone quarry. In the northwest part of Mound township the rock dips northwest with a 

 throw, or twist, which, by slightly changing it, brings it soon below the surface. Indeed there 

 seems to be a succession of ridges, or swells, with low, changeable dip, though the most observ- 

 able is to the northwest. These ridges are not covered with gravel or sand like some ridges 

 east of the Coteau, under the operation of glacial forces (ice and water), but while they occupy 

 the grand divide of the county, they are nearly bare on their tops and along their slopes, or are 

 thinly covered with a gravelly loam, while the drift, even the stony clay that has been attributed 

 to ice, occupies the valleys between to the thickness of at least 30 or 40 feet. 



All over these ridges, which vary from a quarter of a mile to three or four miles in length, 

 and are for the most part thinly covered with soil and tuif, there are little nests of large blocks of 

 quartzyte piled so together that they seem to have been thrust up from below by some force. The 

 edges of these blocks are squarely broken off, and slope toward each other, i. e., toward the center 

 of the pile, while the blocks themselves lie so that their upper surfaces slope in all directions away 



