240 GEOLOGY OF THE BLACK HILLS. 



covering the slopes and rocky ridges. For nearly twenty miles this stream 

 flows in a general easterly course, crossing the slate and quartzite forma- 

 tion at right angles to the bedding of the strata. Where the hard quartz- 

 ites predominate in the hills, the creek has cut a deep gorge or canon 

 through them; but where the softer clay-slates prevail in extensive belts, 

 the stream flows through an open valley, inclosed by low rolling hills and 

 bordered by broad level flats of grass land. Finally, entering a cafion in 

 the limestone formation near the foothills, the water sinks among the 

 bowlders in the bed of the stream and disappears, from whence a dry 

 arroyo, fringed with trees, continues to the plains. 



In the Spring Creek district I include, for convenience of description, 

 all the area of the Hills drained by that stream, and also a district of clay- 

 slates northeast of Harney Peak, giving rise to a small branch known as 

 Whiskey Creek, flowing six to eight miles south of Spring Creek, in the 

 same direction, and sinking in the foothills. 



The head branches of Spring Creek drain an area of nearly one hun- 

 dred and fifty square miles, elevated about 6,000 feet above the sea, char- 

 acterized by low, rounded hills and ridges, wooded with pine of medium 

 size, interspersed with numerous small parks and grassy valleys, well 

 watered by the springs and brooks forming the sources of this stream. The 

 prevailing rocks of this region are mica-schists, often garnetiferous and 

 merging in all gradations into talcose and quartz -schist and strata with thin 

 slate-like lamellae, containing but traces of mica. 



Quartz occurs, distributed abundantly in the schists as thin segregated 

 veins, parallel to the bedding, or in irregular bunches, not continuous in the 

 strata. It is found crystalline, white, red, or rose tinted, and, with the 

 exception probably of gold, appears to be' free from any other minerals. 



The abundance of quartz forms a serious annoyance in prospecting for 

 ledges, the whole country being covered with float quartz of every variety, 

 rendering it difficult to trace fragments found to contain gold to the veins 

 from which they were derived. The first tests for gold on Spring Creek 

 were made on a small branch flowing west from Harney Peak and empty- 

 ing into the main stream about three miles above Newton's Fork. The 

 gravel, resulting from the wash of the granite of the Harney Peak range, 



