OF THE 22nd of apeil, 1884. 
31 
vibrations ” are thus produced.; and in the present earthquake the 
shock was probably felt at many stations on account of their 
marginal situation. Thus at Maldon the shock seemed to follow 
the river Black water, and in London it was especially distinct at 
various places along the Thames. In the area of structural damage 
the alluvial flats and marshes slope too gradually to the sea for 
effects due to marginal vibrations on the coast-line to be observed; 
but the numerous records from places round the south and east 
coasts are suggestive of the movement having been exaggerated at 
these stations on account of their marginal situation. There is 
also a certain preponderance of stations at which the shock was felt 
situated along lines of outcrop, and more especially along the 
escarpments of the Cretaceous series, which favours the view that 
these places were shaken by marginal vibrations, reinforced 
possibly at some places by junctional vibrations. No certain 
connection has been traced between lines of faulting and the 
distribution of the shock. 
The velocity of propagation of earthquake-movement depending 
upon the elasticity of the rock-material, geologists naturally called 
attention to the older, harder, and more elastic rocks which under¬ 
lie the newer and softer formations of this country; and I think 
that it may be safely concluded that the westward extension of the 
shock was as it were exaggerated by the spreading of the older 
rocks in this direction; but the connection is not very clearly de¬ 
fined. Towards the western limits of the shock the older rocks 
come near to, or actually crop out' at, the surface, and towards 
these limits there is a large preponderance of records from the 
older geological districts, and moreover the action of the older 
rocks in spreading the shock is apparently shown by all the extreme 
stations being either on Palaeozoic formations or very near their 
outcrops.* 4 ] 
Some very curious effects of the earthquake upon underground 
waters may now be mentioned. At Colchester, for instance, which 
is pretty near the centre of the disturbance, the supply of water in 
the deep wells sunk into the Chalk had been falling off for some 
months previous to the shock, so that it had been decided to deepen 
them, but after the shock the water rose in them over seven feet, 
and this increased level was maintained for over six months, after 
which it commenced to gradually diminish, and it has now got 
almost down to its former level again. This has been accounted 
for by Mr. C. E. De Kance, Secretary to the Underground Waters 
Committee of the British Association, in this way—that the shock 
caused a widening of the fissures through which the water circu¬ 
lates in its course down to the Lower Chalk, and thus, by an 
increased flow, gave rise to a general increase of level in these 
water-bearing beds, from which the wells derive their supply. 
The gradual return of the water to its old level may indicate that 
* The above account of the geological aspects of the earthquake I have con¬ 
densed from the author’s complete ‘Report,’ in which the subject is very fully 
treated in all its bearings. —Ed. 
