Shaler.] 254 [March 7, 
upper slopes of the Blue Mountains had their soils along with 
tlie forests which covered them precipitated into the valleys below. 
Judging by this test we may affirm that a large part of tlie area 
included within the Appalachian district of North America has 
not V)een within the last few thousand years shaken by great 
earthquakes. The condition of the soils lying on steep slopes in 
this region excludes the hypothesis of violent seismic action. 
Tlie most important and on some accounts the best preserved 
indices of earthquake movements in any inland district are found 
where the topographic conditions due to the action of erosion have 
produced more or less numerous detached columns of rock, the 
needles and ])illars which are so often found on the front of a 
great escarpment. The effect of an earthquake shock on the 
more instable of these natural obelisks is often very great. The 
process of decay generally brings those columns into a state of 
extreme instability before they give way under the influence of 
their own weight. In an effort to establish conclusions on these 
features, the observer must take pains to note whether the 
instability be real or not, for the eye may often be deceived and 
misjudge the resistance which a mass may o})pose to disrupting 
forces. With a little care, however, it is easily ascertained 
whether or not a detached mass is a good seismometer. Thus in 
the Appalachian Mountains south of the glacial belt, there are 
many districts where we can prove that a shock of any consider- 
able violence would necessarily overturn scores of isolated frag- 
ments which have evidently occupied a very instable position for 
some thousands of years. They afford substantially tlie same 
evidence as to immunity from earthquakes Avhich the frail gothic 
spires of northern Europe give for the centuries since their erec- 
tion. On the banks of the Kentucky River, at various points in 
the Cumberland Mountains and northward to central Pennsyl- 
vania, I have observed natural obelisks which seem to me to afford 
an irrefragable evidence that intense earthquakes have not affected 
tliat region for some thousands of years. So far as I have been 
able to observe the regions of known seismic activity in southern 
Europe, I have failed to find any such detached masses in a simi- 
lar instable condition. 
Evidence of the same general nature, though on the whole less 
conclusive, may be found in any of the numerous caverns of this 
country which contain extensive masses of stalactite. These ac- 
