CONDITION OF THE FLOOR OF THE OCEAN. 315 



It thus happens that, at the present time, over nearly the whole floor 

 of the ocean wo have mingled in the deposits the remains of organ- 

 isms which had lived under widely different physical conditions, since 

 the remains of organisms which lived in tropical sunlight, and in 

 water at a temperature above 80° F. all their lives, now lie buried in 

 the same deposit on the sea floor, together with the remains of other 

 organisms which lived all their lives in darkness and at a temperature 

 near to the freezing point of fresh water. 



MARINE DEPOSITS ON THE OCEAN FLOOR. 



The marine deposits now forming over the floor of the ocean present 

 many interesting peculiarities according to their geographical and 

 bathymetrical position. On the continental shelf, within the 100- 

 fathom line, sands and gravels predominate, while on the continental 

 slopes beyond the 100-fathom line, blue muds, green muds, and red muds, 

 together with volcanic muds and coral muds prevail, the latter two 

 kinds of deposits being, however, more characteristic of the shallow 

 water around oceanic islands. The composition of all these terrige- 

 nous deposits depend on the structure of the adjoining land. Around 

 continental shores, except where coral reefs, limestones, and volcanic 

 rocks are present, the material consists principally of fragments and 

 minerals derived from the disintegration of the ancient rocks of the 

 continents, the most characteristic and abundant mineral species being 

 quartz. River detritus extends in many instances far from the land, 

 while off high and bold coasts, where no large rivers enter the sea, 

 pelagic conditions may be found in somewhat closer proximity to the 

 shore line. It is in these latter positions that green muds containing 

 much glauconite, and other deposits containing many phosphatic 

 nodules, have for the most part been found; as, for instance, off' the 

 eastern coast of the United States, off' the Cape of Good Hope, and off 

 the eastern coasts of Australia and Japan. The presence of glauco- 

 nitic grains and phosphatic nodules in the deposits at these places 

 appears to be very intimately associated with a great annual range of 

 temperature in the surface and shallow waters, and the consequent 

 destruction of myriads of marine animals. As an example of this 

 phenomenon may be mentioned the destruction of the tile fish in the 

 spring of 1882 off the eastern coast of North America, when a layer 

 feet in thickness of dead fish and other marine animals was believed to 

 cover the ocean floor for many square miles. 



In all the terrigenous deposits the evidences of the mechanical action 

 of tides, of currents, and of a great variety of physical conditions, 

 may almost everywhere be detected, and it is possible to recognize in 

 these deposits an accumulation of materials analogous to many of the 

 marine stratified rocks of the continents, such as sandstones, (juartz- 

 ites, shales, marls, greensands, chalks, limestones, conglomerates, and 

 volcanic gfrits. 



