Vol. 62.] AN UNCONFORMITY IN THE COAL-MEASURES. 



545 



samples are numbered off at convenient lengths on the abscissae, 

 exhibits clearly the relationships just described. 



Fig. 13. — Diagram exhibiting the relationship in composition 

 between the weathered and the univeathered rochs. 



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IV 



At the very base, the Table-Iiocks Sandstone is extremely hard 

 and compact, and its under-surface, which rests upon the eroded 

 shales, is marked by peculiar knobs and sinuous ridges. This hard 

 rock passes rapidly upwards into the ordinary softer massive sand- 

 stone, which when weathered shows concretionary structure on a 

 large scale, the oval segregation-patches being much redder than 

 the surrounding rock. Chemical analysis shows a concentration of 



