10. 
TRANSPORTATION AND DEPOSITION OF 
SEDIMENTS 
Turbidity currents. It has been found that beds as much as 10 
feet thick of fairly well sorted sand are of frequent occurrence in sediments 
at abyssal depths hundreds of miles from the continents. Evidence in the 
cores indicates that these sands have been laid down in water of essen- 
tially the same depth as that which now covers them, 
Characteristic minerals and organic remains in the sands point 
to the continental shelf and slope as the sources from which the sands 
have been derived. The fact that sands and even gravels are found in the 
bed of canyons, but neither on the sides nor the divides, indicates that 
these coarse clastic sediments have been transported along the canyon 
beds by some kind of gravity induced flow. 
Transportation by turbidity currents seems to account for all the 
observed facts. This evidence for transportation of large volumes of 
sediment by turbidity currents through the canyons gives strong support 
to the theory that the canyons themselves have been eroded by turbidity 
currents, 
Cores from Puerto Rico Trough, Since the flow of turbidity 
currents is determined by bottom topography, it is becoming more and 
more possible to predict the nature of the sediment in a given area from 
a knowledge of the bottom topography. 
One of the first of many examples for testing this theory was a 
series of cores taken in and about the Puerto Rico Trough. The result 
was a complete confirmation. Two cores, about 25 miles apart, were 
taken on the flat floor of the trough at 7970 m, (4360 fms.) depth. Both 
