THE MATERIALS OF STRATA. 



39 



away sand ; but sand may be carried out to a dis- 

 tance of more than 50 miles from the shore. The 



Fig. 



-Laminated vertical land iand)of Alum Bay in 



the Isle of Wight, showing current bedding. 



size of the particles of sand when coarse is X of 

 an inch ; but the majority of the grains vary from 

 -j-J-g- of an inch to -5-^-5- of an inch in diameter. 



When a sand is laid down it is incoherent. It 

 often shows evidence of its shallow-water origin, 

 in the manner in which currents have brought its 

 materials from different directions. After a de- 

 posit of sand is uplifted, and exposed to the action 

 of rain-water flowing through it, it begins to be 

 bound together by a cement which determines its 



