72 GEOLOGICAL BIOLOGY. 



ond, transportation of the fragments by water; and, in the 

 transportation, third, separation of fine from coarse and 

 further rounding of the individual grains; fourth, sedimenta- 

 tion under water in layers or strata. The materials for each 

 stratum have gone through these various processes of water- 

 action. The result is that the present characters of the strata 

 have been determined by (a) the nature of the source of 

 materials, (b) the rate., direction, and force of the activity of 

 the water, and (c) the relations of the bottom of the ocean 

 to the surface, or the depth of the water. Each of these 

 three conditions is variable and generally is the same for only 

 a limited area. To illustrate : We know from observing the 

 phenomena of an ocean beach that the beach material where 

 the shores are low and composed of soil is made up of the 

 wash of the shore. If a large river empties in the vicinity, 

 the shore is made up of fine silt and mud ; if, on the other 

 hand, the shores are hard rocks, the beach is composed of 

 coarse pebbles and gritty sand, the result of the disintegra- 

 tion of the rocks themselves. If we examine the shore ma- 

 terial of Florida, where calcareous rocks alone are exhibited, 

 we find the sand composed of broken shells and corals. This, 

 when filled by deposited calcite carried into the interstices 

 in solution and hardened, becomes a calcareous rock, called 

 coquina, and finally a compact limestone. 



Again, if we examine the materials lying on the beach 

 at high tide and those on the bottom out to a depth of a 

 hundred fathoms, we find that the coarse pebbles and boulders 

 are distributed along the line of most violent wave-action 

 near shore, then gravel, and further out only fine sand, and 

 finally only the finest silt appears. This sorting is entirely 

 co-ordinate with the change in violence and rapidity of normal 

 motion of the water in waves and currents. The more rapid 

 and violent the motion of the water, the larger the particles 

 moved and transported by it, and, hence, the farther out 

 from its source the material is borne, the finer and less in 

 amount will be the resulting deposit. 



For all fragmental material the land surface, where it 

 comes in contact with water in motion, may be regarded, in a 

 general sense, as the source, and, in a general way, distance 



