41 



the movement, both horizontal and vertical, that has taken 

 place in connection with the clay-filled fissures seems to have 

 been made possible by the yielding of the materials within the 

 coal seam itself. 



That the coal offered accomodation to the strains that caused 

 the formation of the fissures is shown by the fact that within 

 the coal seam the smaller fissures often divide into a 

 number of branches which eventually die out without passing 

 entirely through the bed. 



The clay filling the fissures is thought to have been pressed 

 downward through the break in the cap rock and roof shale 

 into the coal from the bed of gray shale or soapstone overly- 

 ing the cap rock. As this clay was forced downward into the 

 fissures it caught the overhanging and unsupported edges of 

 the cap rock, roof shale and coal, bending those edges down- 

 ward on the overhanging side of the fissure. 



That this clay was, for the most part, squeezed downward 

 from above the coal horizon is indicated by the manner in which 

 the upper edge of the coal seam overhanging the fissure has 

 been bent downward to a much greater extent than the lower 

 edge of the coal on the foot-wall side has been forced upward. 

 It is shown in the fact that fragments of black shale from the 

 roof of the coal are commos in the clay filling of the horse- 

 back several inches below the top of the coal seam; and frag- 

 ments of coal also occur in the clay some inches below the 

 bottom of the seam. In no case were coal fragments found in 

 the clay filling at a level higher than the top of the coal. 



SUGGESTED ORIGIN OF THE CLAY SEAMS. 



It is thought that the formation of these clay filled fissures 

 was intimately related to the character of the beds above the 

 number 5 coal. It is probable that the character of the under- 

 lying fire clay, which here is dry and does not creep readily, 

 is also a conditioning factor. The fissures were not formed, as 

 at present, until after the vegetal mass composing the coal 

 seam had been compressed to near its present volume. This 



