148 Mr D. Milne on Earthquake- Shocks felt in Great Brltian 



water charged with the finer particles of decayed vegetables 

 from the adjacent peat-bogs. 



" The light pulverulent appearance of some of the floating 

 particles, would incline one to suspect that it was the product 

 of combustion. The extent of the phenomenon, and its oc- 

 curring at different seasons, will scarcely admit the practice 

 of burning the heaths as the cause. It is true that the car- 

 bonaceous particles might be lodged on the moors for some 

 time, and transported by high winds a considerable period 

 after the burnings. 



" Can it be the product of any species of sublimation, caused 

 by subterranean heat \ Its frequent occurrence in a district 

 so often shaken by earthquakes, which has so evidently sympa- 

 thized with remote volcanic action, would rather favour this 

 hypothesis. 



" The volatilized carbon might find its way, on the wings of 

 gaseous emanations, through fissures too minute to afford the 

 phenomena of smoke ; and the source of the internal heat 

 might be too distant to give rise to any other volcanic phe- 

 nomenon. — I am, my Dear Sir, very truly yours, 



" Thos. Stewart Traill.\ 



" David Milne, Esq." 



In regard to the origin of this black powder, it would be 

 perhaps premature to form a very decided opinion till the re- 

 lative proportions of carbon, argil, silica, and iron, existing in it, 

 have been communicated. That it comes from the atmosphere, 

 however, seems already quite clear. That it is not derived 

 from the smoke of houses or muir-burnings, seems also to be 

 made out. May it not be derived from the surface of the 

 ground, the finer particles of which are, it is well known, very 

 frequently carried up into the atmosphere by whirlwinds, and 

 even by evaporation only \ 



In the Comptes Rendus for 1841, two occasions* are men- 

 tioned, when, first at Vernet (in the eastern Pyrenees), on the 

 17th February 1841 ; and second, at Genoa on the 18th Feb- 

 ruary 1841, rain fell, charged with dust : and it is a remarkable 

 coincidence that, on the last of these occasions, there was an 



♦ C. B. p. 62 and 218. 



