DEPOSITION in 



laminae will be thin and close together and the rate of deposit 

 extremely slow. 



In all waters there is abundance of life, most of the forms being 

 provided with skeletons, shells, or tests of some kind. When they 

 die the hard parts fall to the sea bed, and if not destroyed they 

 will lie flat on this bed until buried up in the accumulating sedi- 

 ment. Then they may be preserved and their mode of occurrence 

 in the silt will be exactly the same as that of the well-known 

 fossils which may so often be collected from beds of sandstone or 

 shale. The bulk of the organisms so buried and fossilised will be 

 those which have lived in the water above ; but others will be 

 drifted or blown in : Thus, mingled with a majority of marine forms 

 of life, there may be remains of terrestrial plants, fresh-water, 

 terrestrial, and even aerial animals. 



As all mechanically denuded matter is arrested comparatively 

 near to the shore-line, it might at first be supposed that there would 

 be nothing to cover the bare sea bed beyond this distance. But 

 there is no limit to the distance dissolved matter can travel ; and 

 the composition of sea water shows that it is everywhere present 

 in about even proportions. Some of it remains permanently 

 in solution. But some, like carbonate of lime, phosphate of lime, 

 and silica, is taken out of solution by animals or plants to build 

 their tests or skeletons. Hence their remains, while mingling with 

 the mechanical deposits within the " mud line/ 7 will be the 

 exclusive possessors of the sea-bed outside that line, and here may 

 give rise to calcareous, siliceous, or phosphatic, organic deposits. 



Many deposits of this class are known. A very large area of 

 the ocean floor is covered with a pale, sticky, deposit known to 

 sailors as " ooze." This on examination is found to be chiefly made 

 of remains of calcareous foraminifera (Fig. 10), mingled generally 

 with varying proportions of shells, many of floating or free- 

 swimming forms. Other deposits are formed by corals, others by 

 dead shells, some by calcareous algae, by Crustacea, sea-urchins, 

 fish-bones, sponge-skeletons, diatoms, or radiolaria. These are all 

 organic deposits, having sometimes a calcareous composition like 

 limestones, sometimes phosphatic, and sometimes siliceous like 

 cherts or kieselguhr. 



The site of organic deposits and of the different varieties of 



