1328 EUGENE McDERMOTT 
surface itself. In general, it is possible to predict the ease or difficulty 
with which the reflection method may be applied by a study of the geo- 
iogic column. Well defined hard limestones with shale and sand, especial- 
ly shale, above them, may be depended on to give good reflections, where- 
as poorly defined, broken, and siliceous limestones without definite shale 
breaks may offer difficulties. 
Where the reflecting stratum is sloping, as in Figure 10, if the slope 
is sufficiently great, the reflection may arrive at the recorder farthest 
from the shot point sooner than at the nearest recorder. Where slopes 
are sufficiently great, this method may be used to determine slope and, 
where correlation is difficult, it may be used as an aid to correlation. 
Where the presence of a fault is suspected it may be possible to 
arrange the recorders and shot point so that the fault bears the relation 
SHOT FPPECOROLE FS 

FAULT eS) h 
IIc. 11.—Retlections across fault. 
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