14 A Yorkshire Rector of the Eighteenth Century. 



remains had not yet been discovered. That Michell, without 

 that key, should have been able to work out the stratigraphical 

 succession over the southern half of England with so near an 

 approach to accuracy entitles him to be ranked as the most 

 eminent of the English predecessors of William Smith in this 

 department of geology. 



Further interesting proof that the Rector of Thornhill 

 continued to make fresh detailed geological observations until 

 late in life is supplied by a long and still impublished letter 

 from him to Henry Cavendish, dated 14th August, 1788. 

 This document, together with the draft of the reply to it has 

 been preserved among the Cavendish papers. The corres- 

 pondence shows that between the years 1783 and 1793 Caven- 

 dish, in company with Dr. Blagden, was engaged in tracing the 

 distribution and succession of the geological formations in the 

 southern half of England. In the course of the journeys which 

 this investigation involved, questions arose on which Michell's 

 experience could be of service. When thus appealed to, he, 

 with his usual generosity, gave in ample detail the results of 

 his own observations. His letter to Cavendish, written on 

 his return from one of his journeys to London, told how he 

 had halted for a night at an inn on Greetham Common, and 

 when there, was surprised to find a deposit of clay in the 

 midst of the ' yellow limestone,' of Cavendish and Blagden, or 

 what was afterwards known as the Oolitic series. From his 

 careful description it would seem that this deposit was a 

 patch of the Chalky Boulder-clay of that district, containing 

 scattered flints and pebbles, which he thought might support 

 a conjecture he had formed as to the origin of flints in general. 

 As to the nature of this conjecture the letter is silent. The 

 writer seems to have taken this boulder-clay to be one of the 

 argillaceous bands which are intercalated between the members 

 of the ' yellow limestone,' though he had never noticed it be- 

 fore. In previous correspondence Michel! had pointed out that 

 this ' yellow limestone ' is underlain by the ' Lyas.' He now 

 insists upon the importance of this sequence which, he says, 

 runs into Leicestershire in the south, and can be traced on the 

 north to where the Trent falls into the Humber, and across the 

 upper part of the Humber. He shows that there is another 

 ' yellow limestone ' in his district of Yorkshire, which must 

 lie far below that of Cavendish and Blagden. He points out 

 that there is ' no Lyas anywhere under it or near it to the 

 westward of it, all the way from Leicestershire, by the edge of 

 Nottinghamshire and Derbyshire and a long way into Yorkshire, 

 and how much farther I don't for certain know. In many 

 places, if not everywhere, the coal is found under our yellow 

 limestone, through which they sink in many places to come 

 at it.' Michell had thus traced the extension of what is now 



Naturalist, 



