564 DEEP-SEA DEPOSITS. 



of a calcareous nature, like tlie foramiuifers, others of a siliceous nature, 

 like the spicuhe of sponges, the radiolaria, and the diatomacea. 



In these muds are found solid concretions from 1 to 4 centimeters in 

 diameter and embedding all the organic and inorganic elements of the 

 sediment. Chemical analysis has demonstrated that the cement of 

 these concretions consists princi]>ally of phos])hate of lime. 



The sediments with the phosphatic nodules present the greatest 

 resemblance to certain well-known strata belonging to various stages 

 of certain series, especially of the cretaceous period, viz, the green 

 sandstone, the glauconitic sandstone, the white chalk. The resem- 

 blance, which is not only in the nodules, but also in the sediments 

 which contain them, is such that there is evident similarity in their 

 mode of formation. 



In regard to the origin of this phosphate of lime, the simplest idea 

 and the one that everything confirms is that it is derived immediately 

 from the decom])Osition of animal debris buried in the sediment after 

 death. Their form is destroyed by the elfect of the reactions of the 

 sea water upon them. 



GENERAL OBSERVATIONS. 



The expedition of the Challenger deserves the gi'atitude of science, 

 not alone because it has shed light upon important facts in the province 

 of physical geography, and because it has furnished many new ideas 

 of the animal and vegetable life that people the abysses of the ocean. 

 The nature of the bed of those abysses, vast areas whose depth exceeds 

 4,000 meters and sometimes attain more than 8,000 meters, was, but a 

 short time ago, hardly known to us. Deposits formed from the terra 

 firma observable not far from continents do not continue in the abys- 

 mal regions, where the motions of the sea, to which marginal deposits 

 owe their origin, exert no influence. 



In those regions, mineral particles ui)on which the meclianical action 

 of the water has left an imprint are not to be found, but instead vol- 

 canic and pulverized matter, as well as clayey substances i)roduced by 

 their chemical decomposition, the Avhole mixed with remains of micro- 

 scopic organisms. Such are the deposits which cover the largest part 

 of the sub-marine crust of the globe. 



We see for the first time the principal outlines of a geological map 

 of the sea bottom, showing the manner in which the diflerent types of 

 deposits are distributed upon the great ocean beds. This ma}) is 

 annexed to the volume; it contains, in synoi)tic form and in convention- 

 alized colors, the results of more than two thousand soundings made 

 at depths greater than 2,000 meters.* 



Among other facts which appear from the map iu question, the first 

 to attract the attention is how much the abyssal deposits exceed the 



* There were 1,600 of these soundings iu the Atlantic, 300 in the Indian Ocean, and 

 400 iu the Pacific. 



