262 ELEMENTARY GEOLOGY 
but when the rivers are in flood, what they transport 
often changes to a coarser material, perhaps even to 
a sand, because then the river water is able to carry 
coarse fragments. Here then, at this time, layers of 
sand are deposited, while during ordinary conditions 
= ie j : 
ences Ge: 3 
— ——- 
Fic. 149. 
Lamination in stratified rock. Tiny fault in upper left-hand corner. 
the deposit is of clay, and so layers of sand and clay 
alternate in the growing accumulation. 
Again, rivers often change their point of overflow, 
particularly when they enter the sea over deltas. At 
one time the sediment may be that which the river is 
carrying, while later, when the mouth of the stream 
