BIG STOKE AND LAC QUI FABLE COUNTIES. 619 



Cretaceous shale.] 



foot of the lake, rock can be seen on the southwest side at two points, rising plainly above the 

 general level of the bottoms, and ascending in the slope from the prairie.'' 



Below Lac qui Parle no outcrops of rock were observed in this county. Its next exposures 

 found within the Minnesota valley are nine to twelve miles southeastward, where gneiss occurs 

 in small ledges one mile west of Montevideo and close south of this town, and in extensive out- 

 crops one to two miles farther southeast. All these are in Chippewa county, on the northeast 

 side of the Minnesota river, opposite to the east end of Camp Release, the next eastern township 

 of Lac qui Parle county. 



Cretaceous shale. The granite and gneiss of this district are probably 

 in many places overlain by Cretaceous beds, but no exposures of them have 

 been discovered within the limits of these counties. A layer of shale of 

 this age that outcrops on the Dakota side of the Minnesota river, very 

 nearly opposite to the northwest corner of Big Stone county, is described 

 by Prof. Winchell, as follows:* 



"About a half mile, a little west of south from the stage station at the head of Big Stone 

 lake, in Dakota, an exposure of Cretaceous occurs in the right bank of the upper Minnesota. It 

 shows superficially only a weathered, sliding talus of shale, which is black and somewhat 

 slaty, but which on digging becomes moister and soft and somewhat flexible, yet parting into 

 small chips. Over the surface of the ground, where this shale outcrops, the turf is prevented 

 from growing, and two conspicuous objects, weathered out from the shale, are seen. 1st. Little 

 angular crystals of pure gypsum, the largest seen weighing not over half a pound. 2d. Little 

 angular bits of yellowish red ochre, that are hard and thin, but can be cut with a knife. There 

 is also an occasional piece of brecciated, clayey, or at least aluminous rock, the cracks and sur- 

 faces of which are filled and coated with crystals of cale-spar. When broken by the hammer, 

 these part along the numerous planes that on either side are lined by this calc-spar, and each 

 fragment is entire, appearing itself a mass of calcite. It is only by several attempts that a view 

 of the interior, on which these coatings are formed, can be obtained. The thickness of this 

 shale bed cannot be ascertained. The angular bits of ochre are most numerous near the top, 

 where the drift supervenes, but the gypsum crystals are scattered over the whole outcrop. The 

 indications are that the gypsum and ochre are embraced within the shale, and become superficial 

 by weathering. The whole may be twenty-five feet thick. 



"This shale bed is the cause of a terrace in the descent from the high prairie, and of numer- 

 ous springs that issue below the drift, about sixty feet below the prairie level. These springs ex- 

 cavate narrow ravines and 'gulches' in the shale, the whole being smoothly turfed over, except at 

 the point above described. These alternating gulches, and the intervening short pieces of the 

 remaining terrace, make the bluff in general appear hilly, in its ascent from the bottomland. 

 These ravines, in the wet season of the year, are very soft, and since they appear practicable for 

 a horse, are the cause of many misfortunes to the traveler. Many such treacherous, springy 

 places are described as occuring along the shores of lake Traverse, at some elevation above the 

 waters of the lake. The same rolling ascent from the bottomland to the high prairie can be seen 

 also at the head of Big Stone lake, on the Minnesota side, and it is there doubtless due to the 

 same cause." 



Glacial and modified drift. 



The ledges of granite near the foot of Big Stone lake are quite remark- 

 ably glaciated, having been planed, rounded and worn smooth by ice which 

 moved from northwest to southeast, as shown by the direction of large 

 grooves and hollows on the rock-surface and by its being most noticeably 



'Second annual report, p. 190, 



