668 J. A. UDDEX COMPOSITIOX OF CLASTIC SEBIMEXTS 



Beach gravels and sands. 



Harbor silts. 



Sediments on the landward side of the Atlantic continental shelf. 



Sediments on the seaward side of the Atlantic continental shelf. 



Sediments fi'om the submerged west coast of America. 



Sediments in the Bering Sea. 



Sediments in the sea near volcanoes. 



Sediments near the margins of ocean basins. 



Beach gravel. — The few samples of materials sorted by beach action 

 show the effectiveness of sorting by riparian currents. In six samples 

 99 per cent of the material is confined in three, or two, grades. In the 

 averages of the seven samples the maximum grade contains 60 per cent. 

 It will be recalled that beach material from lakes and rivers were better 

 sorted than most other sediments in continental waters. 



List of Saniples in Talle 13 



114. Beach gravel, Olivia, Texas. 



115. Gravel, mostly granite, Marblehead, Massachusetts. 



116. Beach gravel, Olivia, Texas. 



117. Ocean beach, Dutch Harbor, Alaska. 



118. Beach gravel, Olivia, Texas. 



119. Beach gravel, Olivia, Texas. 



120. Ocean beach, Douglas Island, Alaska. 



Silts in harbors. — Thirteen samples were taken from mud adhering 

 to anchors of vessels lying in the harbor of Baltimore in February, 1893. 

 The mud represents the sediments in the places where the anchors had 

 last been lifted. Information on this point was obtained in each case 

 from the captains of the ships from which the samples were obtained. 

 Silting is going on in most harbors. Harbor waters are quiet. As a 

 class these sediments are finer in their mechanical composition than any 

 other marine sediments examined. The chief ingredient is very fine 

 sand in one sample taken from near Salem, Massachusetts; in five sam- 

 ples it is coarse silt ; in three it is medium silt, and in four it is fine silt. 

 In the assortment of their admixtures the samples resemble each other 

 quite closely. Excepting the coarsest sample, no less than six grades 

 contain more than 1 per cent of the whole sample. In the general aver- 

 ages of the admixtures, the coarse grades decrease a little more rapidly 

 than the fine for the five admixtures nearest to the maximum. This is 

 believed to be a characteristic of sediments formed in waters with pro- 

 gressively slackening currents, which are waters that are overloaded. In 

 the coarsest grades represented there is in several samples an increase in 

 quantity away from the chief ingredients. This is in most cases due to 



