and especially in Scotland. 149 



earthquake-shock. It is stated in this last account that the dust 

 fell, not only on the day of the shock, but on that preceding and 

 on that following it ; and that for about a month previously, 

 there had been an enormous quantity of rain, and a very low 

 barometer. The dust which fell, both at Vernet and at Ge-* 

 noa, was analyzed, and found to consist of the ingredients 

 composing the porphyritic rocks of the country, the quantity 

 of each ingredient bearing a tolerably near proportion to the 

 relative quantities in the rocks themselves. 



The opinion mentioned in the Comptes Rendus, as enter- 

 tained by those who made the analysis and attended to the 

 phenomenon, was, that by a " trombe d'eau," or some such 

 phenomenon, the debris of the rocks had been carried up into 

 the atmosphere in a state of minute division, and then brought 

 down by rain. Is a similar explanation not applicable to the 

 black powder which falls in the mountainous districts of Perth- 

 shire? The clay-slate formation undoubtedly possesses all 

 the elements except one, of which Dr Traill found the powder 

 to be composed ; and this one element, viz., carbon, which is 

 not in that rock, may readily have been derived from the peaty 

 covering of the hills. How these particles were carried up 

 into the atmosphere, it is not difficult to conceive ; for, besides 

 the suction of an ascending water-spout, as suggested in the 

 Comptes Rendus, there must be often in these mountainous 

 regions, whirlwinds or eddying currents of air quite capable of 

 carrying up earthy matters ; and, indeed, the mere effect of 

 evaporation from the soil would be sufficient for that purpose. 



If these views be correct, there is no connection, at least of 

 a direct nature, between the falling of the black powder and the 

 occurrence of earthquake-shocks in Perthshire. It is true 

 that water-spouts and whirlwinds are connected with sudden 

 changes in the electrical state of the atmosphere ; and thus 

 there may be a remote connection between these phenomena 

 and earthquake-shocks, if the latter are attributable to elec- 

 tricity : but this is a point which has not yet been established. 



(2.) The next circumstance deserving notice, is a peculiar 

 smell or odour, which was perceived by many persons at or 

 about the time of the earthquake shocks in October 1839. 



Thus, Sir John Mansel, who felt the great shock of 23d Oct. 

 1839, in Comrie House, ^ays, that, towards the termination 



