DISCOVERY BY REFLECTION SEISMOGRAPH 57 
bad surface conditions and the presence of a creek branch near the 
well, to shoot exactly at this point below the well. For this reason, we 
are not entirely certain whether the well is on the up throw or the 
down throw side of this small fault, but suspect from a calculation 
of each trace of the records shot between 11 and 14 which shows a 
steep east dip east of 14, that the well is on the up throw side. 
COMPARISON OF ORIGINAL WORK WITH DETAILED WORK 
An examination of the two maps reveals that in most places where 
seismograph points have been duplicated, the two methods have 
_yielded almost identical results. This is not true, however, on the 
road near the axis of the structure where the original work shows 
points about 20 feet higher or slightly more than .003 second differ- 
ence in corrected time. Since we are now comparing absolute depths, 
we are depending upon a good calibration shot across the dry hole 
as well as satisfactory work along the axis of the structure. With the 
correlation type shooting, only one determination under one single 
weathering condition is obtainable at every reflection point. With the 
detailed method, several reflection points are averaged to determine 
the datum at the shot point, as described above. In short, a com- 
parison of the maps indicates that the original work was entirely 
satisfactory work of its type, but was not spaced closely enough to 
secure adequate data on this area of small structure and steep dips. 
IDENTIFICATION OF THE REFLECTION 
When the well, St. Cyr No. 1, reached the Viola formation, veloc- 
ity tests were made by lowering the detector into the well and shooting 
on the surface. The total depth of the hole at this time was 2,801 feet, 
or a distance of 8 feet in the Viola limestone. Velocity tests with the 
shot point at a distance of 250 feet from the well were entirely un- 
satisfactory, due to energy traveling directly to the casing and creat- 
ing a disturbance on the geophone which obviated any possibility 
of getting satisfactory velocity information. Accordingly, two new 
shot points were chosen, one 500 feet southwest of the well and one 
500 feet northeast. Unfortunately, these were drilled only to a depth 
of 30 feet, but good velocity records were obtained nevertheless (see 
Fig. 9). This velocity information shows the average overall velocity 
to the Viola limestone to be approximately 10,600 feet per second. 
The reflection on the record 1-SW. commencing at .548 second, must 
therefore be identified as being from the base of the Mississippi 
301 
