268 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [April 10, 



per second (or about double that of the great Neapolitan earthquake 

 of 1857), then 



, , 900 28-1 n. n 



^^^^ ~2~ ' 

 1-92 X 14-06 = 26-99 feet ; 



so that it would readily rise above, and flow over the surface of the 

 great clay-bed through the fissures therein, assuming that to be 

 from 30 to 40 feet thick. If any severed mass of the clay-bed, as C, 

 be free to move laterally upon the ooze-bed towards the adjoining 

 one, it is obvious that the water already raised in the fissure /' 

 by the movement impressed in the first semiphase of the wave, may 

 be squeezed up by the approach of D and C, and flow out over the 

 surface of both. 



These calculations are of course but approximations, as it is im- 

 possible to take into account the resistances which the water in the 

 ooze-bed may oppose to being squeezed out from the solid matter of 

 that bed, or the resistance which may be opposed to its rise in the 

 fissures by their form, clogging with sand or silt &c. 



The squeeze thus almost simultaneously given over a vast area of 

 the ooze- or water-bearing bed, though momentary (^. e. lasting 

 usually but for a very few seconds), sets a vast body of water in 

 motion ; and the work accumulated therein is not instantly lost, but 

 has to be gradually expended. It is therefore expended in causing 

 the forced-up liquids to rise beyond the level due to the hydrostatic 

 head, which measures the impressed force, whence the liquid may 

 slowly recede ; or if the forces engaged be sufiicient to raise the 

 liquid column above the earth's surface, it will continue then to 

 overflow for a longer or shorter time. When this overflow ceases, 

 the last portions of the elevated liquid sink back (unless evaporated) 

 through the apertures whence they rose. Should the liquid forced 

 up be sandy ooze, the sand is carried up in suspension along with 

 the water ; and as the volume of the flow slackens, more and more sand 

 accumulates in the aperture of ascent as the water-current gets 

 enfeebled and is no longer able to wash it clean out to the surface ; 

 and in the end, the aperture is left nearly full of sand, down through 

 which the last of the water sinks back, as through an imperfect filter- 

 bed ; and thus, by the ascending current, at first rapid, then getting 

 slower, ceasing, and then retreating partly or wholly through it,, 

 the upper surface of the sand in the aperture gets modified in 

 its form. And should the aperture approach in section to a circular 

 tube or well-shaped fissure, this form tends finally to assume more 

 or less that of a tundish or inverted cone of sand, often washed quite 

 clean from other matter. In a long fissure, several such funnel- 

 shaped cavities may form from point to point. 



Should the water-bearing bed be wholly or in part of slimy but 

 tenacious mud, the mud itself may rise and ovei-flow the surface, as 

 it appears to have done in some of the fissures in this Cachar case, 

 and may remain, as it drains and consolidates, in permanent masses 

 above the surface-level, or it may retreat more or less below that ; 



