218 



THE SEA FLOOR 



in 



decomposition. These manganese nodules vary 

 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 



Fig. 159. — Scalpellum 

 on a Manganese Nodule 

 (" Challenger "). 



Fig. 160. — Spherule with Metallic 

 Nucleus coated with Black 

 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 



