IS94-] 247 [Slialer. 
distribution of these shocks in times anterior to the l)riet' jK'riod of 
which we have any historical record. I have ah-eady made refer- 
ence to the results of tliis inquiry in an article published in Scrib- 
ner's magazine for Marcli, 1887, entitled "The stability of the 
earth." In that paper, however, it was undesirable to treat the 
subject ill any other than a very brief way. I propose in the 
following pages to set forth the methods by which we mn^^ obtain 
some knowledge of earthquake ])henomena in the earliest stages 
of the present geological period with incidental reference to such 
disturbances in former geological ages. 
There are two ways in which violent earthquake shocks produce 
effects which may be observed long after the time when the 
shocks occurred. When these shocks take place beneath the sea- 
floor, they produce, as is well known, a sudden elevation of the 
water in the form of a great disc immediately over the point where 
the disturbance takes place. From this seismic vertical the eleva- 
tion of the water is propagated in every direction in the form of a 
great wave, which though low is veiy wide. Ap])roachiug the 
shore, this wave is heaped up on its front through the fact that the 
shoals retard the movement of the undulation where it comes into 
shallow water, and so causes the following portion of the wave to 
crowd against the preceding portion of the ridge. On the west- 
ern coast of South America and elsewhere along the Pacific shores, 
these waves frequently attain a height of thirty or more feet, and 
owing to their great momentum sweep far up the shore producing 
on the land effects which in certain cases may long remain evident. 
The action of a powerful earthquake shock is recorded in another 
manner. It overturns all instable bodies, such as delicately poised 
masses of stone, those natural obelisks which are frequently 
formed by the processes of rock decay, or boulders which are 
delicately poised in instable positions. IJy carefully observing the 
regions where such natural seismometers remain unshaken we 
may receive important evidence as to the recent distribution of 
these disturbances. 
Considering first the effects of ocean movements induced by 
earthquakes, we find that where they strike the shore, they exert 
a very great amount of energy which causes an overturning of 
any poised bodies which may come within the linuts of their more 
vigorous action. An inundation will also operate to efface any 
delicate topography cast in frail material such as sand, which may 
