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XIII. An Account of the great Derbyshire Denudation. By Mr.]. 
Farey, Sen. In a Letter to the Right Hon. Sir Joseph Banks, 
Bart. K. B. P. R. S. 
Read March 21, 1811. 
Sir, 
1 had but recently entered on the survey of Derbyshire and 
its environs, which under your kind patronage I was induced to 
commence in the autumn of 1807, and had only cursorily exa- 
mined the strata, in my way from Charnwood Forest and Bree- 
don in Leicestershire, in order to meet you at Overton Hall, 
before I perceived clearly, that those principles which con- 
template the terrestrial strata as terminating or ending in one 
direction (simple and important as they are), which I had 
learned uhder Mr. William Smith in 1801, and which he has 
so successfully applied in the filling up of his maps of the 
strata in the south-east and east, and some of the middle parts 
of England, would fail me, in their application to the strata of 
Derbyshire, without taking into consideration along with them, 
not only the denudation, or local stripping off, of patches of 
strata, some of immense extent and thickness, and even more 
considerable than those which I had discovered to be missing* 
* And such as Dr. William Richardson had found to have been removed, in 
several places, from off the basaltic area in the counties of Derry and Antrim in Ire- 
land, and has named abruptions , in his very admirable paper on this district, in the 
Philosophical Transactions for 1808. 
