INTRUSIVE MATERIALS 481 



line of stratigraphic yieltling affected the rocks to remote depths is cer- 

 tainly strongly suggested by the presence of these igneous intrusions. 



There are no known dikes that cut through the surface rocks on the 

 Cincinnati geanticline, either on the Kentucky or Tennessee arches, but 

 there are numerous lead and zinc bearing veins, composed of calcite, 

 barite, and fluorite, that do cut across the Ordovician rocks of these domes. 

 Similar veins in the Kentucky-Illinois fluorspar district are related to the 

 dikes of peridotite, where they cut walls of limestone and are accompanied 

 by faulting. The depths to which the mineral veins continue on the Cin- 

 cinnati geanticline are not kno^ai ; the Chinn vein of calcite and fluorite 

 on the Kentucky Eiver, in Mercer County, Kentucky, passes down into 

 the lowest rocks exposed in Kentucky, the same being the Camp Nelson 

 beds of the Ordovician system. These veins completely fill wide fissures 

 in limetone, and to what extent they have been eroded may never be 

 known; but, in view of the facts brought to light in this paper, the 

 writer suggests the strong proba])ility that beneath these mineral-bearing 

 veins there are intrusions of igneous rock; that the veins were formed 

 from hot ascending solutions and vapors passing upward to the surface 

 along crevices which the intrusions formed, but only partially filled. In 

 the case of the mineral veins of the Kentucky-Illinois district, the dikes 

 came near, if not entirely to, the land surface as it existed at the time of 

 the intrusion; but the peridotite in Fayette County, Pennsylvania, ac- 

 cording to Hice, did not reach the surface. It is found cutting across 

 the Pittsburgh coal bed, where it was discovered in mine workings, but 

 dies out in the Pennsylvanian rocks that overlie the coal. The dikes of 

 Elliott County, Kentucky, are found on tlio surface cutting across rocks 

 of the Coal Measures, Imt whether or not they readied the surface as it 

 existed at the time of tlic intrusion is not known. There are no mineral 

 veins associated with the intrusions, either in Fayette County. Pennsyl- 

 vania, or in Elliott County, Kentucky, for the reason probably that they 

 cut sandstone and shale instead of limestone and did not offer the proper 

 conditions for precipitation and mctasomatic replacement, such as ex- 

 isted in the Kentucky-Illinois district or on the central Kentucky and 

 Nashville arches of the Cincinnati ui)lift, where the veins have walls of 

 limestone. 



BUOAI) GEOLOGIC FEATURES 



A. R. Crandall recognized the importance of considering the broad 

 geologic features in connection with the dikes of Elliott County and 

 pointed out the fact that they are near an east- west anticline which is 



