465 



Mr. Newton gives a synopsis of the stiiita of the lUack Hills, of which 

 the following is a short abstract: 



Jura 2i)0 Clavs iiinl mails, with smne liiiiestoin-. 



Red Bed.s 340 Ked day. 



Carljouit'erous 690 Sandstinies ami limestones. 



Paleozoic : 



Silurian (Potsdam) 250 Silicious sandstoues atid loiigloinerates. 



Archiean ( .') ; ' Slates and schists, with iutfiisive granite. 



Of these the Mesozoic and Paleozoic strata are resting conformably 

 upon each other, the Cenozoic and Arcluean are not. The Black Hills 

 have been formed by the uprising of the Arcluean rocks, which lifted 

 up and broke through the overlying strata. That this uprising must 

 have taken place after the Cretaceous and before the Miocene forma- 

 tions can be seen from the fact that the strata of the latter do not con- 

 form with those t)f the former. 



The Black Hills have received their present form bj' erosion. The 

 softer rocks have worn away faster, leaving the harder standing out as 

 ridges or crags. As the center is raised, the dij) of the strata is out- 

 ward and the outcroppings form concentri(; ovals. The Jurassic clays 

 and marls, the clays of the Red Beds and the slates and schists of the 

 Arcluean formation are comi)aratively soft, while the Cretaceous sand- 

 stone and the granite spurs of Arcluean formation are hard. The 

 Miocene formation belongs to the surrounding plains and does not 

 enter the Hills anywhere. 



The outcrop of the Cretaceous sandstone forms the foothills, and that 

 of the Jura formation and the lied Beds makes the so-called " Race 

 Track," a more or less continuous valley between the foothills and the 

 hills proper. The Race Track is mnch broader on the south side and 

 forms the larger part of the " Miimekahta Plains." On the east side 

 t4ie Carboniferous limestone belt forms a series of hills, and on the west 

 side, where the strata are nearly horizontal, a broad plateau, the "Lime- 

 stone District." As the slates and schist are comparatively soft, the 

 center of the Black Hills is lower, except where the granite or igneous 

 rocks come to the surface and form the highest peaks in the range. 



Ai/rniDEs. 



The plains at the base of the Black Hills have an altitude ol" about 

 1,000 meters. The highest point is the to}) of Harney s Peak, one of 

 the series of granite crags at about the center of the Hills. Its iilti- 

 tnde is given dirtereiitly. The most reliable measurements are without 

 doubt those given by the United States Geological Survey, one of 

 which makes it 7,308 feet, the otlier 7,440 feet, or, respectively, 2,245 



