DEPTHS FROM SEISMIC TIME-TRAVEL CURVES 127 
second beds for each of these points and subtract the corresponding 
time interval for each point. Then draw the two new time-travel 
curves through these points. The slopes of these two new curves will 
give the dip of the surface of the V, bed relative to the surface of the 
V3 bed. The above action will, of course, rotate the plot of the time- 
travel curves through an angle @ so that the abscissa, or distance axis, 
will be parallel to the secondary surface, which is the surface of the V3 
layer, and the coordinates of the time-travel curves must be read ac- 
TIME (N SECONDS 

FAST LIMES TONE H20 % = 5860 
Fic. 4—The time-travel curves obtained from actual data taken from records 
shot in an area in West Texas, and the resulting profile calculated according to the 
method described in this paper. 
cordingly. With this action accomplished, the procedure is the same as 
for the case of a single dipping layer. The dip angle calculated in the 
usual manner will be the angle of dip between the surfaces of the V3 
and V, beds, and the values of k and k will be the thickness of the V3; 
bed under the secondarys hot points on the surface of this bed. The true 
velocity of V4 can be calculated in the same manner as V3 was previ- 
ously determined; and if the result is not in good agreement with the 
assumed value of V4, a new value for this quantity can be assumed 
and the entire procedure repeated. A high degree of accuracy can be 
7187 
