116 Dr. C. Ricketts—Changes in the Earth's Crust. 
would break off (d) and slipping down strike against the opposite 
wall (Fig. 3e) and thus fill up the fissure. An immediate effect of 
the impulse must be the occurrence of an earthquake shock, more or 
less intense, according to such various conditions as the size and 
weight of the falling mass, the space through which it falls or slips, 
the structure of the rocks involved, and other circumstances. If 
from a subsequent change this enlarged area is placed in a restricted 
position, the compression thus caused not only affects to a certain 
extent the dip of the strata, but causes the ‘fault-rock’ included 
within the crevice to be compressed into slabs lying parallel to the 
sides of the fault, forming a coarse but true slaty-cleavage. This 
cleavage is of very frequent occurrence in the north and south or 
main faults in the Triassic sandstone of the district around Liverpool. 
In the Presidential address to the Liverpool Geological Society for 
the Session 1872—1873' it was explained that the occurrence of 
earthquakes (not including some connected with volcanic eruptions) 
was due to the formation of faults, each of which must register at 
least one, or probably a succession of earthquake shocks. The 
examination of strata has as yet discovered no other cause than the 
formation and settling down of geological faults, capable of producing 
all the varied phenomena recorded as accompanying earthquakes, 
including that of the huge sea waves, which not infrequently are 
one of their most destructive accompaniments, when occurring near 
the coast; being probably caused by the rushing of water into the 
trough (Fig.3*) formed by the depression of the faulted mass, immedi- 
ately succeeded by the consequent rebound ; at all events these waves 
are not due to the shock of the earthquake, for some occurring in the 
near neighbourhood of the sea, as in that of Hssex (1884), and in 
North America, at Charleston, §. Carolina (1886), were entirely 
unaccompanied by such disturbances of the water. 
The reporter of an excursion along “ the line between the High- 
lands and the Lowlands,” made in 1875 by the Geological Class of 
Edinburgh University, under the guidance of Professor Archibald 
Geikie, noticed the fact that Comrie, celebrated for its earthquake 
shocks, lies almost directly over the great fault extending across 
Scotland, 170 miles in a direct line from Stonehaven to the Isle of 
Arran. He spoke of this as being ‘the first attempt to connect the 
abundance of tremors at that place with the geological structure 
of the ground underneath.”* Professor J. Milne, F.R.S., of the 
Imperial College of Engineering, Tokio, infers “that in Japan faults 
are still being formed, and that the earthquakes there are to us the 
announcement of these fractures ;”* “also that certain earthquakes 
and faults are closely related phenomena, the former being an im- 
mediate effect of the latter.’* Dr. H. J. Johnston-Lavis, F.G.S.,° 
and Mr. G. K. Gilbert, of U.S. Geological Survey,® refer the oc- 
1 Proc. Liverpool Geological Society. An abstract of this Essay (‘‘ On Fissures, 
Faults, Contortion and Cleavage,”’ by Charles Ricketts) appeared in the GroLoGicaL 
Maeaztne, Vol. X. 18738, p. 202. 
2 Nature, vol. xii. p. 98. 3 Brit. Assoc, Report, 1881, p. 201. 
4 Earthquakes and other Earth Movements, by John Milne, F.G.S , 1886, p. 279. 
5 Nature, vol. xxiii, 1881, p. 498. 5 Nature, vol, xxix. 1883, p. 40. 
