74 ELEMENTARY GEOLOGY 
and so the texture of all strata that are derived by this 
means is that of fine grains. Ice can carry fragments 
of any size, as can the other two agents. Hence rocks 
derived by means of these, can be of any texture from 
finest to coarsest. 
The size of the fragments transported by the wind 
or water will depend upon the velocity with which 
these are moving. Therefore by the action of these 
agents the fragments are assorted into layers, accord- 
ing to their texture, the coarsest being moved only by 
the ‘strong currents, while the finer may settle in quiet 
water or air. This gives rise to banding or stratifica- 
tion (Figs. 26, 82, 85, Plates 4, 6, 7, etc.). Ina 
measure this is true also of the fragments from volcanic 
eruptions, for the larger pieces fall first, and usually 
near the cone, while the finer ash may drift for days, and 
even months, falling scores or hundreds of miles away. 
Ice, on the other hand, carries a bowlder as easily as 
it does a particle of sand; and so ice-formed beds are 
mixed in texture, and not assorted into layers. 
The wind, volcanoes, and ice (glaciers), may build 
beds of rock fragments on the land, or they may sweep 
them into the river, the lake, or the sea. Those beds 
formed by water are deposited under its surface, and 
in most cases are permanently covered by it, although 
on the beach, and on the river floodplains, they may be 
above the water during the greater part of the year. 
