SEISMOLOGICAL DISCOVERY OF VERMILION BAY 53 
by tropical hurricanes, the field crews watch the Coast Guard Weather 
Reports (received by radio) and occasionally have to run for land, re- 
turning later to salvage gasoline drums and boxes of dynamite scat- 
tered over the shore by sudden and severe squalls. 
Even under such conditions, the explorations averaged 200,000 
acres per month; and as much as 15,000 or more acres have been sur- 
veyed in a single operating day. 
VERMILION BAY SEISMIC SURVEY 
Br 
GECPHYSIGAL RESEARS PRPOR ATION 
Seer 
For the Loudkiece ian 

Fic. 1.—Refraction fan layout for exploration of Vermilion Bay. 
In the survey of Vermilion Bay, three recording boats were used. 
Each was equipped with a radio transmitter and receiver, an oscillo- 
graph, and a velocity meter (geophone) recording through a vacuum 
tube amplifier. The timing device was an electrically operated 50- 
cycle tuning fork. The air wave was picked up by a carbon-button 
unit. The resulting records were developed immediately, thus guiding 
the observers in the size of the next shot. The instant of explosion was 
determined by the breaking of a wire wrapped around part of the 
charge of explosive, thus terminating the operation of the shot trans- 
mitter. In general, the charge of explosive was simply lowered to the 
383 
