DISCOVERY BY REFLECTION SEISMOGRAPH 55 
was about 22 feet or .oo4 second, which represents a variation of .o02 
second or about 10 feet from the average. 
SURFACE CORRECTION ZONE 
In this area the time in the surface correction zone of low velocity 
varies from a minimum of .o1o second on the north and east to a 
maximum of .025 second on the southwest. This variation is illus- 
trated by the vertical elapsed time at the shot hole, as shown on map 
D in Fig. 4, which shows a vertical time of only .o12 second for a 
hole depth of 53 feet at shot point 12 toa vertical time of .o25 second 
for the same hole depth at shot point 21. It is noteworthy that the 
variation in surface correction zone time is more than the corrected 
time relief of the structure. 
On the map showing the vertical time in the shot holes, a figure 
has been added showing from the driller’s logs the thickness of the 
alluvium or soil cover, or the depth to bed rock. Except in one or two 
instances, a close correlation may be seen between the increase in 
time and the increase in thickness of the alluvium. The low velocity 
shown in the shot holes 19, 20, and 21 is entirely due to a thickening 
of the alluvium. It is worthy of note that shot point 11 shot east has 
a surface correction zone time of .o1o second for the average of the 
first two traces, while shot west, it has an average of .o1g second. With 
the corrections applied, the determinations for the depth of the Viola 
limestone at shot point 11 differ only .oo2 second from the west side 
to the east side. This indicates quite clearly that an adequate method 
has been used to correct for these abrupt variations in the alluvium 
thickness. The flood plain of the small creek has its boundary about 
too feet east of shot point 11. 
DISCOVERY OF STEEP DIP AND FAULT 
A small fault was discovered between shot points ro and 11, and 
was again crossed between 11 and 14, 16 and 22, and 16 and 18. Fig. 
8 shows the record obtained showing a possible fault with small throw 
lying between shot points 10 and 11. While the amount of displacement 
on the fault is so small that it might have been questioned as due to 
effect of variation in the surface correction zone, it was picked up so 
definitely on the mentioned records that it is believed present. 
The close approach of the syncline on the east to the high point 
at the center of the structure indicates also that an anomalous con- 
dition exists which is the result of this fault. It was impossible, due to 
299 
