198 Prof. W. H. Hobbs—The Charleston Earthquake, 1886. 
As we have elsewhere pointed out,! active craterlets formed in 
connection with earthquakes, like the fissure springs of which they 
are the ephemeral and much overgrown representatives, appear to be 
arranged upon fracture planes, and are located, in many cases at least, 
at the intersections of such planes. If, therefore, we can secure 
a correct map of the craterlets within an earthquake district, this map 
should reveal the outlines, at least, of the fracture system within the 
province. Notwithstanding the fact that an alignment of craterlets 
along earthquake-faults and fissures has been often pointed out, it has 
not generally been thought important to accurately locate them. The 
unique exception is, perhaps, the map prepared by Major Dutton and 
printed in connection with his report upon the Charleston earthquake.” 
A mere glance at the map in question (reproduced with some 
additional lines on p. 199) discloses the fact that the areas con- 
spicuous for craterlets are aligned within zones strongly marked 
out in at least a number of instances. Perhaps the most striking 
examples are to be observed within the area to the south and south- 
west of the station of Woodstock, where the lines trend north-easterly. 
Throughout the district affected, however, similar if less striking 
alignments are to be observed. Such lines mark out lanes of 
maximum disturbance at the surface, and through them we are 
enabled to study the distribution of surface intensity of shocks in 
connection with the Charleston earthquake. 
We are in this instance, further, especially fortunate in having 
another excellent guide to the surface distribution of seismic intensity, 
and one the full significance of which seems to have been overlooked. 
The ‘epicentral tract’ is crossed by three radiating lines of railway 
which afford well-distributed sections along which location is especially 
accurate. Grading the intensity of the shocks is furthermore facilitated 
along the line of the railways for the reason that a structure of 
essentially uniform elasticity and rigidity extends throughout the 
sections. The examination of the tracks to collect the evidence upon 
the distribution of damage was made by Mr. Earle Sloan, apparently 
a very careful observer. The report shows that sometimes for miles 
within the ‘epicentral tract’ the tracks reveal little, if any, serious 
damage, but such areas of little disturbance are succeeded by relatively 
narrow zones within which fish-plates are torn out, joints opened, and 
in a very considerable number of instances the tracks are thrown into 
a local ‘kink’ or S-shaped distortion. No simple law was found to 
determine the intervals between successive points of such maximum 
derangement to the track, but Major Dutton has drawn the conclusion 
that upon each railway line the distribution of damage indicates 
a central maximum from which the intensity falls away upon either 
side by a law expressed in a very simple reversed curve whose form 
resembles the Hogarthian line of beauty, and has been named by him 
an indicator. 
1 W. H. Hobbs, ‘‘ Topographic Features formed at the time of Earthquakes, and 
on the Origin of the Mounds in the Gulf Plain’: Amer. Journ. Sci., 4th ser., 
vol. xxiii (1907), pp. 245-256. 
2 Loe. cit., pl. xvi. 
