218 



THE SEA FLOOR 



decomposition. These manganese nodules vary in 

 form and size in different localities ; at one place they 



may be large, subspherical, 

 and smooth, resembling a lot 

 of potatoes ; at another place 

 smaller, like marbles ; at 

 another place large and 

 spherical, but the external 

 surfaces rough to the touch, 

 owing to the numerous mam- 

 millations (Fig. 159) ; at 

 another place flattened with 

 one side rougher than the 

 other ; and at yet another 

 place the nodules take the 

 form of huge slabs. With the 

 manganese nodules are usually 

 associated, especially in deep 

 water far from land, numerous 



FlG. 159. SCALPELLUM FlG.l6o. SPHERULE WITH METALLIC 



ON A MANGANESE NODULE NUCLEUS COATED WITH BLACK 

 ("CHALLENGER"). MAGNETITE, SUPPOSED TO BE OF 



COSMIC ORIGIN ("CHALLENGER "). 



teeth of sharks and ear-bones of whales, impregnated 

 and coated more or less thickly by the peroxides of 

 iron and manganese. In the Red Clays, also, numerous 

 minute magnetic spherules (Fig. 160), some with 



