58 OLDHAM: THE CACHAR EARTHQUAKE OP 1 0'fH JANUARY 1869. 



with the surface, and forcing up of liquid matter, might be accom- 

 panied by the evolution of large quantities of gas which carrying with it 

 spray and dust might, viewed through the light of a vivid imagination, 

 produce all those appearances of fire, smoke, and sulphurous vapours 

 which have been so often and so graphically described. 



All these causes above described, however active and however power- 

 ful, are essentially transient, and soon the normal pressure is re-established 

 in the water-bearing stratum; the water which has been forced up 

 immediately begins to rush back, carrying with it the edges of the 

 fissure at which it escaped, and ultimately leaving a funnel-shaped 

 opening, either single or grouped with others, which is in fact the 

 so-called 'crater/ 



In the case of this shock the matter forced up was not pure water, 

 but water charged with sand, a circumstance which has produced some 

 important modifications in the aspect of these openings. Instead of 

 the crack or opening through which the sand and water rose being left 

 comparatively open or only choked by the debris of its sides, as soon 

 as the current began to slacken there was deposited in and around 

 its mouth a quantity of sand which has modified, and to a great extent 

 reduced, the action of the water in rushing back again; the sharply 

 washed and furrowed aspect produced by the water is only visible 

 near the top of the aperture where the sand has been washed down, 

 while the bottom, instead of narrowing down almost to a point, is broad 

 and nearly flat, though slightly hollowed; this feature being produced by 

 the filling up of the fissure with sand, through which the water filtered 

 back as through a filter bed. The nature of these craters is shown 

 in pi. VI fig. % ; a a represents the raised rim of sand, sloping gradually 

 outwards, which is deposited round the mouth; from a to b represents 

 that portion whose aspect is due mainly to the wash and scour of 

 the water rushing downwards, and which is at most merely coated with 

 a film of sand; the strong lines from a to b are continued downwards to 

 show what would probably have been the form, had there been no sand 

 forced up, while the slightly curved line connecting b b is the cross 

 ( 58 ) 



