12 A Yorkshire Rector of the Eighteenth Century. 



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 

 immediately 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 exceed a few yards in thickness.' The same 

 accurate observer likev/ise noticed the abundant divisional 

 planes, known now as ' joints ' ; also the occurrence of disloca- 

 tions or ' faults,' wherelDy ' the whole set of strata on one side 

 of a cleft are sunk down below the level of the corresponding 

 strata on the other side.' He was aware of the frequentl}" 

 inclined position of the stratified formations, and pointed out 

 that their inclination increases towards the mountains which 

 generally, if not always, are formed out of the lower, and there- 

 fore older rocks. 



These and other observations detailed in his Earthquake 

 memoir relate, indeed, to some of the more obvious and 

 elementary facts of geological structure, but they had never 

 before been made and described so clearly. They served com- 

 pletely to disprove the theory of tumultuous deposition by the 

 Flood, and they paved the wa}^ for the establishment of the 

 principles of stratigraphical geology, based on organic remains, 

 afterwards worked out by the genius of WilHam Smith. But 

 Michell proceeded to build on his accumulated observations 

 a brilliant illustration by which he indicated his conception 

 of the manner wherein, by successive extensive movements 

 and prolonged denudation, the crust of the earth, as he knew 

 it in England, might have acquired its internal structure and 

 superficial aspect. Following his characteristic experimental 

 habit, he proposed the construction of a model which would 

 place his conception in visible form. ' Let a number of leaVes 

 of paper,' he said, ' of several sorts or colours, be pasted upon 

 one another ; then bending them up together into a ridge in 

 the middle, conceive them to be reduced again to a level surface 

 by a plane* so passing through them as to cut oft" all that part 

 that had been raised ; let the middle now be again raised a 

 little, and this would be a good general representation of most, 

 if not all, large tracts of mountainous countries, together with 

 the parts adjacent, throughout the whole world.' 



Regret has been expressed that Michell, whose only pub- 

 lished geological essay was so remarkable, did not make further 

 contributions to a branch of natural history for which he 

 showed so great an aptitude. Sir Charles Lyell, in referring 



* Such a plane would in nature be produced by prolonged denudation. 



Naturalist, 



