NATURAL SCIENCE. 



and mineral particles too small for precise determination. These 

 fine washings do not make up a pure clay, but a substance allied to 

 bole-clay rich in iron and manganese. 



The loo-fathom contour is taken as the more or less arbitrary 

 boundary separating the deep-sea from the shallow water deposits. 

 This contour line divides the continental masses from the great 

 oceanic depressions. The area of the ocean between the shore and 

 the loo-fathom line is about ten millions of square miles, whereas 

 that between the loo-fathom and 500-fathom lines is only seven 

 millions. The area between the two last-mentioned contours may, 

 therefore, be spoken of as the continental slope. 



Marine deposits in general are classified as follows : — 



Deep-sea deposits beyond 

 100 fathoms. 



/ Red clay. 

 Radiolarian ooze. 

 Diatom ooze. 

 Globigerina ooze. 



Blue mud. 

 Red mud. 

 Green mud. 

 Volcanic mud. 

 Coral mud. 



Shallow- water deposits be-1 



tween low-water mark gands. gravels, muds, &c. 

 and 100 fathoms. I 



Littoral deposits between] 



high- and low - water I Sands. gravels, muds, &c. 

 marks. 



Pelagic deposits formed 

 in deep water far away 

 from land. 



Terrigenous deposits 

 formed in deep and 

 shallow water close to 

 land masses. 



) 



The following table indicates the average depth at 

 of the more important deposits is found, the average 

 carbonate of lime present, and the area of distribution : — 



Red clay . . 

 Radiolarian ooze 

 Diatom ooze 

 Globigerina ooze 

 Pteropod ooze 



Coral mud 



Coral sand 

 Other terrigenous deposits 



Mean depth 

 in fathoms. 



2,730 



2.894 



1.477 



1.996 



1,044 

 740 1 

 176/ 



1,016 



Mean per- 

 centage of 

 Ca CO3. 

 670 



4 01 



2296 



6453 

 79 26 



8641 



19 20 



which each 

 amount of 



Area, 

 sq. miles. 



51,500,000 



2.290,400 



10,880,000 



49,520,000 



400,000 



2,556.800 



16,050.000 



It is with the deep-sea deposits alone that the authors of the 

 present volume are concerned. These cover more than one-half of 

 the earth's surface, and pass gradually into the shallow-water deposits. 

 Phenomena of erosion are almost entirely absent from the deep sea, 

 and the only mechanical actions of any consequence are those con- 

 nected with submarine volcanic eruptions. • The effects of chemical 

 action, on the other hand, are strongly marked by the occurrence of 

 glauconite, phosphatic nodules, manganese nodules, and zeolites. 



