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The Occurrence of Hand-specimens of Jointed Structure in 

 THE New AiiBANY Shale. 



Glenn Citlbertson, Hanover^ Ind. 



About one and one-half mili-s northwest of the village of Kent in 

 Jefferson County. Indiana, and near the entrance to Lloyd's Cave, there 

 is an outcrop of the New Albany black shale. Tliis outcrop is found for 

 some distance along the east and west road, and also along the road 

 extending in a northwest direction past the upper entrance of the cave. 

 One stratum of the shale, which is somewhat more indurated than the 

 others, and which is approximately one-half an inch in thickness, furnishes 

 excellent specimens of jointed structure. Both master and minor joints 

 run so close together as to leave the weatliered remnants of the shale 

 in pieces from four to eight inches long and from two to six inches wide. 

 The joint planes ax'e approximately parallel, although in some cases there 

 is considerable variation from parallelism. 



Such specimens furnish excellent illustrations of jointed structure 

 for museums and for the classroom, and are very convenient. The accom- 

 panying photograph shows several typical specimens, as found weathered 

 out and lying on the surface. The relation of master and minor joints and 

 the sharp outlines of the specimens are clearly indicated. 



The number of specimens is seemingly rather limited, but further ex- 

 amination may disclose many more. So far as the writer is aware, the 

 occurrence of such perfect specimens of jointed structure in sizes con- 

 venient for handling is very unusual if not entirely unique. 



