4 8 The Badland Formations of the Black Hills Region 



Mr. J. B. Hatcher in 1893 recorded the great abundance of 

 chalcedony veins in the Titanotherium beds and states that they 

 occur only in certain localities of limited area,. never more than a 

 few square miles in extent. He does not mention dikes. He attri- 

 butes the chalcedony filled fissures to shrinkage caused by the 

 gradual dissipation of the water that has been entrapped during 

 the process of deposition and thus necessitates contraction with- 

 in the sediment and considers that the vertical fissures thus 

 formed beneath the original surface were later filled by chalce- 

 dony, occasionally calcite or Iceland spar, dissolved out of the 

 overlying beds by heated waters percolating through them.* 



In 1894 Mr. E. C. Case found many dikes and veins in the 

 Badlands, and in the American Geologist of the following year 

 gives the results of his observation. He says the sandstone of 

 the dikes in the Oreodon beds is not hard, but soft and friable, 

 and seldom shows much weather resisting tendency. The. color 

 of the dikes is a light green and easily recognized as identical 

 with that of the greenish Metamynodon sandstone found at a 

 lower level. He adds also that the material in the dikes of the 

 Titanotherium beds is universally from some strata below. He 

 describes the dikes as commonly perpendicular and extending in 

 a straight line across the country, but without any common direc- 

 tion or parallelism. Some of the dikes were traced continually 

 for more than a mile, the thickness seldom reaching more than 

 three inches. Reference is made to others reaching as much as 

 eighteen or twenty inches. 



Concerning the veins he says : "Where the veins of chalce- 

 dony occur alone, they are so perfectly analagous in form and 

 position with the dikes as to make it evident that the joints and 

 cracks they occupy are of the same origin as those of the dikes. 

 * * * From their hardness they resist weathering a great deal 

 longer than the soft clays and stand up in jagged lines above 

 the surface. When the clay around is removed and the support 

 fails, pieces are broken off from the thin seams and fall on the 

 neighboring clays ; thus whole hills are covered with small sheets 

 of quartz and are protected as by a shingle roof from the action 

 of rain. * * * When the veins meet and cross they do not pene- 

 trate and destroy each other, but fuse, and perfect homogenous 

 crosses were obtained from localities of such intersection." 



Referring to instances where the dike and vein features 

 were closely associated, he says : "In the cases where the dikes 



*Am. Nat. Vol. 2 7, 1893. 



