South Dakota School of Mines 47 



by rock masses without any immediate influence either of heat 

 or of solvent action. These clastic bodies are known as dikes 

 also. 



Until recent years, but few instances of clastic dikes had 

 been observed., and geologists appear to have o 1 * erlooked the 

 earliest statement of their occurrence in the Badlands. Prof. F. 

 V. Hayden says that in May, 1855, about ten miles northeast of 

 Eagle Xest Butte., he observed "a vertical seam of fine-grained 

 sandstone passing through the different strata for several 

 hundred yards, varying in thickness from forty to thirty inches. 

 Sometimes this vertical seam is left standing, the more yielding 

 calcareous marl having been washed away from either side., and 

 thus it forms a high perpendicular wall having much the ap- 

 pearance of mason work. It is composed of a fine, light gray 

 grit, and is doubtless due to the infiltration of fine sediment in 

 l fissure in the strata."* 



Two years later, October 8, 1857. Prof. Hayden found a 

 similar dike between the Cheyenne river and White river, made 

 up of fine blue grit and vertical to the enclosing strata. In connec- 

 tion with this he states that a large number of these ''curious 

 seams'' occur at different localities. 7 It is to be noted that Prof. 

 Hayden did not confuse these with the far commoner chalcedony 

 veins, for he says (October j) that on the left side of the Chey- 

 enne, fifteen miles above the mouth of Bear creek, "Dissem- 

 inated all through the Oreodon bed in every direction are thin 

 seams of silex in the form of chalcedony.'' 



Many years later Prof. Robert Hay of Kansas, described 

 two dikes near Chadron. One of these averages ten inches in 

 thickness, but to this should be added two and one-half to five 

 inches on each side, this latter material being made up of vertic- 

 ally laminated and fluted clays. Its traceable length is 120 feet, 

 the direction X48E. The other dike averages thirteen inches 

 thick, plus three inches of vertically fluted clays on each side 

 and is traceable 100 feet, the direction X70E. Prof. Hay 

 regarded the dikes as having been intruded from below and com- 

 pared them to the phenomena of mud volcanoes. * 



*Hayden. F. V. Notes on the Geology of the Mauvaises Terres 

 of White River. Nebraska (now South Dakota) Proc. Phil. Acad. Sci., 

 1857-8, p. 156. 



iHayden, F. V. On the geology and natural history of the Upper 

 Missouri. Trans. Am. Phil. Soc, Vol. 12, 1862, pp. 3 0-31. 



iHay, Robert. Sandstone Dikes in Northwestern Nebraska. Bull. 

 Geol. Soc. Am., Vol. 3, 1892, pp. 50-55. 



