personally to examine Michell found that 

 the rocks everywhere displayed a striking 

 order and regularity. The earth, he wrote, 

 "is not composed of heaps of matter 

 casually thrown together, but of regular 

 and uniform strata. These strata, though 

 they frequently do not exceed a few feet, 

 or perhaps a few inches, in thickness, yet 

 often extend in length and breadth for 

 many miles, and this without varying 

 their thickness considerably. The same 

 stratum also preserves a uniform character 

 throughout, though the strata imme- 

 diately next to each other are very often 

 totally different. Thus, for instance, we 

 shall have, perhaps, a stratum of potter's 

 clay ; above that a stratum of coal ; then 

 another stratum of some kind of clay ; 

 next a sharp grit-sandstone ; then clay 

 again ; and coal again above that ; and 

 it frequently happens that none of these 

 exceeds a few yards in thickness. There 

 are, however, many instances, in which 

 the same kind of matter is extended to 



