On the Cause of the Earthquakes in the Ionian Isles. 119 



which falls to powder in water, of that kind which prevails in 

 the Ionian islands, in Sicily and in Calabria, after having been 

 dried by exposure to the air, was put into a vessel, having two 

 apertures with stopcocks, by means of one of which small quan- 

 tities of water might from time to time be admitted, whilst the 

 other communicated with a bent tube containing coloured spirit 

 of wine, which served as a gauge to measure any expansion of 

 the air or other materials in the vessel. This prepared appara- 

 tus was left several hours undisturbed in a room without a fire, 

 to allow of every part of it acquiring the temperature of the 

 room ; the first stopcock was suddenly turned, and water admit* 

 ted, and, after a few seconds, again closed. Now, watching the 

 gradual absorption of the water by the masses of marl, and their 

 falling to powder, I witnessed a decided, though not very con- 

 siderable, rise of the spirit in the bent tube, in the direction indi- 

 cating an expansion within the vessel. Various trials were made 

 with the t»ame general result : the details I cannot give, for my 

 note-books have not yet arrived from Malta, nor indeed is it ne- 

 cessary, for they would be tedious, and, to those acquainted with 

 Buch inquiries, perhaps of little moment. It may be sufficient 

 to say that I was tolerably satisfied the expansion indicated 

 arose from no other source than the absorption of the water 

 by the clay, and that there was noi to my knowledge any cause 

 of error present to vitiate the conclusion ; however, as there 

 might have been, I hope the experiment will be repeated, and 

 on a scale in regard to magnitude, commensurate with its im- 

 portance. 



Allowing the result to be correct,^ that clay or marl actually 

 expands from the absorption of water, the application of the 

 fact is obvious in relation to the production of earthquakes, in si- 

 tuations, 'as already mentioned, in which there are large beds of 

 these substances under the earth^'s surface. The volume of these 

 beds undergoing change equally, from the less absorption and 

 loss of water, they may be a constant cause of motion, or of 

 earthquakes, wherever they exist, the motion varying in degree 

 according to a variety of circumstances, which it may be diffi- 

 cult to appreciate, as the quantity of water absorbed, the time 

 in which it is absorbed, the pressure of su})erincumbent strata, 

 &c. and the accidents connected either with the eflTects of i>ent 



