WATER DEPOSITS 669 



the presence of a small amount of cinders from the furnaces in steam 

 craft, and does not necessarily characterize natural deposits in similar 

 localities in the sea. 



List of Samples in Table I4 



121. Silt from the bottom of the harbor at Salem, Massachusetts (close to 



Marblehead). 



122. Silt from the bottom of the harbor at Fortress Monroe, Virginia. 



123. Silt from the bottom of the mouth of the James River, Virginia. 



124. Silt from the bottom of the harbor at Port Antonio, 14 mile from shore, 



West Indies. 



125. Silt from the bottom of the Great Wicomico, Chesapeake Bay. 



126. Silt from the bottom of the harbor at Hampton Roads, Virginia. 



127. Silt from the bottom of the harbor at Fall River, Massachusetts. 



128. Silt from the bottom of the harbor at Rio de Janeiro, South America. 



129. Silt from the bottom of the harbor near Baltimore, Maryland. 



130. Silt from the bottom of Providence Harbor, Rhode Island. 



131. Silt from the bottom of the mouth of South River, Chesapeake Bay. 



132. Silt from the bottom of the harbor at Stilton Quarantine Station, below 



Baltimore, Maryland. 



133. Silt from the harbor at Sea Wall, Atlantic coast. , 



Deposits on the continental shelf in the West Atlantic. — Sedimenta- 

 tion on the continental shelf east of the United States is probably not as 

 rapid now as in some earlier ages. It is perhaps less rapid than in the 

 Gulf of Mexico. Some of the material in samples from this part of the 

 sea is organic, consisting of fragments of shells and corals and of entire 

 tests of foraminifera. These materials are evidently subjected to trans- 

 portation and sorting by currents on the bottom of the sea. In the case 

 of a few samples, where the organic ingredient was considerable and 

 where it consisted of elements whose sorting appeared the least doubtful, 

 corrections have been made to eliminate their quantities from the analy- 

 ses. These corrections were made by ascertaining the ratios of these two 

 ingredients in each grade by a separate count of the two in a part of the 

 grade. 



The 21 samples examined have their maxima distributed among vari- 

 ous materials as follows : 



Diameter of grains Nurr.ber of 



in millimeters. samples. 



Fine gravel 2-1 2 



Coarse sand 1 -1/2 3 



Medium sand 1/2 -1/4 2 



Fine sand 1/4 -1/8 4 



Very fine sand 1/8 -1/16 4 



Coarse silt 1/16-1/32 5 



Medium silt 1/32-1/64 1 



