reports on the subject. By far the most 

 important contribution to the scientific 

 discussion of the nature and cause of 

 these earth-tremors was this paper by 

 Michell. It contained the first attempt 

 to suggest a natural cause of earthquakes, 

 and to explain the nature of seismic 

 movements. 



In attacking the problem Michell 

 started with the fundamental postulate 

 of the existence of " subterranean fires." 

 It was the general belief of the day, which 

 he shared, that these "fires* 3 resulted 

 from the spontaneous ignition of pyritous 

 inflammable strata, such as coals and car- 

 bonaceous shales lying at variable dis- 

 tances beneath the surface of the earth. 

 Werner and his followers were so con- 



. 



vinced that such was the origin of these 

 "fires," to which they attributed the 

 existence of volcanoes, that they believed 

 volcanic action to be of comparatively 

 late date in the history of the globe, seeing 

 that it could not arise till vegetable 

 26 



