DYNAMICAL GEOLOGY. 2 17 



the soundings, and a general map is drawn representing their 

 geographical distribution. 



The deposits due to the mechanical action of water are 

 almost entirely of terrigenous origin. River detritus and the 

 sand and mud produced by wave action are floated seaward 

 and spread on the floor by the action of marine currents. 

 The blue colouring matter in terrigenous deposits is sometimes 

 an organic substance, sometimes iron sulphide ; the green 

 colour is due to glauconite, the red colour to yellow iron ore. 

 On the coasts where volcanic rocks predominate, marine mud 

 consists of finely triturated volcanic material. The pelagic 

 " Red Clay " so widely distributed in the Pacific and Indian 

 Oceans as a rule occupies the deeper stretches of the ocean- 

 floor. According to the investigations of Murray and Renard, 

 deep-sea " Red Clay " is essentially composed of strongly de- 

 composed volcanic material, originating partly from subaerial, 

 partly from submarine eruptions, and also contains "numerous 

 remains of whales, sharks, and other fishes, together with 

 zeolitic crystals, manganese nodules, and minute magnetic 

 spherules, which are believed to have a cosmic origin " (see 

 Murray, "Oceanography," Geographical Joiirnal, 1899). The 

 Red Clay deposits pass, in most places, quite gradually into 

 the calcareous oozes. 



A special interest attaches to the chemical changes that take 

 place in the waters of the ocean or the ocean-floor by the 

 action of the sea-water upon the various kinds of sediment. 

 The zeolitic, manganitic, and phosphatic contents of the Red 

 Clay betray what an important part has been played by 

 chemical interchange in determining the actual constitution of 

 this extensive deposit. The more accurate knowledge of the 

 ocean-floor has thrown a flood of new light upon all researches 

 regarding the deposits of past geological epochs, their correla- 

 tions, their origin, their constitution, their subsequent trans- 

 formations, chemical and dynamical. It is not too much to 

 say that the Challenger Expedition marks the grandest scientific 

 event of the nineteenth century. 



Chemical Deposits in Water. Chemical, technical, medical, 

 and geological works have published innumerable analyses 

 of the chemical deposits separated in springs, underground 

 water, rivers, and lakes. Gustav Bischof summarised the 

 most important results of this extensive literature in his 



