Marine Muds and Nodules 139 



animals inhabiting the bottom of the sea. In doing so the 

 mineral matter of which it consists comes in contact with the 

 organic secretions of the animals, mixed with sea-water, and is 

 ground up along with them in the milling organs of the animals. 



The Reducing Action of organic matter on sulphates has 

 long been known, and its importance as an agent in geological 

 metamorphosis was thoroughly recognised by Bischof 1 . 



The effect of Trituration in promoting the chemical decom- 

 position of silicates by water was demonstrated by Daubre 2 , 

 more particularly in the case of Felspar. I found the observa- 

 tions to hold good also for Augite. Clear crystals of this 

 mineral from the Tristan da Cunha group, when pulverised 

 with water in an agate mortar, rendered the water alkaline 

 to turmeric paper. 



It is evident therefore that at the bottom of the sea a number 

 of conditions occur together, which are favourable to the 

 production of chemical change. The ground animals, in the 

 search of food, pass the mud through their bodies, grinding 

 it up, and bringing it thoroughly into contact at the moment 

 of comminution with the sea-water and the digestive secretions 

 of the animal. The action of these secretions on the sulphates 

 in the sea-water is to produce sulphides, and the action of 

 the sulphides on the ochreous matter of the bottom is to pro- 

 -ulphides of iron and manganese. Even if the bottom 

 were covered with felspathic or augite sand, the sulphides, 

 acting on these silicates in the moment of partial decomposition, 

 would convert the ochreous oxides by degrees into sulphides. 

 tin- volcanic material, lava, dust, scoriae, pumice, whirl) 

 forms the bulk of the unaltered matrri.il of the bottom of 

 the ocean, is so dealt with by the animals, is rvidriit from 

 the specimen from the Pacific on the table, which i< not a 

 -prciinrii. hut rather a typical one. 



acted what nutrimrnt they can from the mud, 



the animals reject it. containing a < nt.iin proportion of sulphides 



manganese. These snlphi<l I \v-ll known. 



* Bischof, Lehrbuch der Chemischen und Physikalischcn Geologie (1863). 



358 



* Daubrte, Geologie Experimental*, I. 268. 



