in all directions may travel thousands of 

 miles before becoming so feeble as to be 

 no longer sensible to ordinary observation. 



n. The Structure of the Stratified Part 

 of the Earth's Crust 



The most important part of Michell's 

 Earthquake paper, considered as a land- 

 mark in the history of geological science, 

 is the account which it contains of what 

 is now known as "the crust of the Earth." 

 Earlier in the century John Strachey 1 

 had shown that in the south-west of Eng- 

 land the materials of the visible part of 

 the earth had not been promiscuously 

 accumulated, but had been laid down in 

 a recognisable succession which he traced 

 in due order from the Coal up to the Chalk. 

 He further perceived that while the coal 

 strata are all more or less inclined, their 

 upturned edges are overlain by the Red 

 Marl and later formations in horizontal 



1 Phil. Tram. vol. 30 (1719), p. 968; vol. 31 



(1 7*5), P- 395- 



- 



39 



