75 



average and the median is the central value of all median 

 diameters in the depth interval. In each interval, the 

 mean usually becomes greater than the median as the spread 

 of values larger than the median increases. 



The median and mean of median dieuneters increase with 

 depth in the interval from 2 5 to 100 feet. Also in this 

 interval, the values greater than the median are spread 

 considerably more than those that are smaller. This increase 

 with depth and exaggeration toward high values is due to the 

 fairly large amounts of relic sediment, particularly coarse 

 red sand, which occur in this depth range. From 100 feet to 

 175 feet the median diameters show a decrease. In the range 

 from 125 to 175 feet, the median and mean values for the ' 

 median diameters are almost identical and the highest and 

 lowest values show a narrow range. These depths correspond 

 to the most widespread areas of fine-grained sediment on the 

 shelf and the change of character in the curves indicates 

 present day sedimentation and contemporary covering of older 

 deposits as has been discussed in preceding sections. The 

 effect of relic material evident in other zones is not shown 

 in this depth zone. From a depth of 175 feet to 300 feet, 

 the median diameters show a general increase and a wide spread 

 of values higher than the median due to the occurrence of 

 relic material, authigenic minerals and rocks, and coarse 

 shell fragments in this depth range. The coarse gravels, 

 indicated by dredging, cannot be shown on this diagram, since 

 complete samples were not retained for analysis, but their 

 effect would be generally to cause a high maximum value of 



