OP SAND FOEMATIONS ON MARINE COASTS. 11 



Diameter of grains in millimeters. 



Fine dust or silt . 02 — . 03 



Medium dust or silt . 03 — . 05 



Coarse dust or silt . 05 — . 1 



Finest sand 0.1 — 0.2 



Pine sand 0.2 — 0.3 



Medium sand 0.3 — 0.5 



Coarse sand 0.5 — 1 



Grits 1 — 2 



Gravel 2 — 4 



Coarse gravel 4 — 6 



Pebbles 6 — 10 



Coarse pebbles 10 — 20 



S'hingle 20 — 50 



Stones 50 —250 



Boulders 250 — Upwards. 



The limit of the coarseness of sand grains is here considered as 

 0.2 — 0.1 mm. When the grains are finer than 0.05 mm., the soill) 

 has lost the physical properties of sand. It does not feel gritty to the 

 fingers, and if it is dropped on a level and hard surface the grains 

 will not separate but congregate in small heaps. It needs several minutes 

 to sink in water to the bottom of a test tube. When over 0.05 mm. 

 the soil has, however, more of the characteristics of real sand. It is 

 then gritty, when pulverized between the fingers. If scattered dry, it 

 will separate into grains conspicuous to the naked eye. When mixed 

 with water in the test tube, it sinks rapidly, usually in less than one 

 minute, and it is to a noticeable degree conductive of water. It is 

 difficult in practice to draw the lower limit for sand of a certain coarse- 

 ness, because the soil is more or less mixed. On account of the difference 

 in specific gravity of the grains many samples contain grains of different 

 grades. 



In the above table the measurements of diameter refer to the average 

 sized grains in each class. The term sand has here been applied to soil, 

 the graias of which are under 1 mm., while a coarseness of 1 — 2 mm. 

 has entitled the soil to the name of grits. When the chief ingredient 

 is particles larger than 2 mm. and below 6 mm. the soil has been 

 designated as gravel. 



Common sand is 2,100 times heavier than dry air, while only 2.5 to 



1) The term soil is in this paper used in its broadest technical sense to 

 designate the loose material constituting the disintegrated superficial layer." 

 of the earth's surface. 



