Shaler.] 256 [March 7, 
the close of tlio glacial period. In tiie iiortliorn section, we 
have numerous poised boulders often occupying positions where 
they have never been supported by forest trees. Sometimes a 
large boulder bears a small one riding u])on the top of it, 
affording a natural seismometer of considerable sensitiveness. 
In other cases, as before described in our consideration of sea- 
waves due to earthquakes, these boulders are poised on the 
borders of steep-faced hollows into which they would inevitably 
have been precipitated by any considerable movement of their 
bases. It is often possible to start these fragments down their 
slopes even where they have the weight of tons, with a very 
slight amount of displacing force. South of the glacial belt, 
wherever the escarpments are of a nature to yield detached 
masses in the process of decay, we almost always find them and 
often in an extremely instable condition. Natural bridges, over- 
hanging precipices, tottering on their fall and occasionally giving 
away under the influence of the atmosphere, caverns charged with 
stalactites, very steep slopes with a uniform covering of soil, all 
point to the same conclusion, viz., that a large part of this 
Appalachian region has long been exempt from devastating 
shocks. In a similnr way, the region about our great lakes 
and a large part of the Cordilleran district north of Mexico 
afford indications of long-continued repose. Such regions as the 
Saxon-Switzerland in Europe, and generally the topographic 
character of the region north of the Alps, point to the same con- 
clusion. On the other hand the whole of the Itnlian peninsula, so 
far as I have explored it, seems to indicate, by the absence of soil on 
steep slopes and the lack of instable erosion columns in front of 
the escarpments, the action of powerful earthquake shocks. 
It appears to me that the foregoing suggestions as to the 
evidences of former earthquake activity beneath the seas and 
upon the land surfaces may fairly be made a matter of deliberate 
inquiry. It is worth our while to know the seismic history of a 
district, not only on account of the scientific questions involved, 
but also because earthquakes are at present by far the most 
unforeseeable of all calamities which beset life. If we could in 
any way determine the enrthquake record of a country foi- the 
period say of ten thousand years in the past, Ave should be in a 
better position to predict tiie chance of recuri-ence of shocks 
within the given field. 
