134 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES 



depth over a considerable area, this also in the Indian Ocean 

 and the Paciiic south and north of the equator. Excluding 

 cones, buried or but little above the surface of the water, the 

 average depth of the whole ocean bed is but little more than 

 IS.OOO feet. 



The results of ocean exploration are numerous and interest- 

 ing, but there is only time now to go briefly over them. If we 

 leave out of account the local effects of inflowing rivers and 

 the changes induced by living agents along the coast and the 

 borders of islands and more or less submerged cones— i. e., ex- 

 cluding the shallow water areas — there is not nnieh diver- 

 gence in the composition of sea Avater. And the same holds 

 good with respect to depth as well as latitude and longitude. 

 That is to say, however much the water of the ocean may vary, 

 from point to point, in temperatnre, pressure or otherwise, it 

 has about the same chemical ingredients, although there may 

 be differences in density. 



At the surface of the ocean plant-life is far more abundant 

 than at any point on land. Within 600 feet of tiie surface, plant 

 life is profuse but not below that depth, which is the limit 

 of light penetration. At deeper levels, down to the maximum 

 depth of the floor, animal life exists, and this is fairly prolific 

 at the very bottom. All the animals there are of the type 

 of mud-grubbers and many of them are provided with or- 

 gans especially adapted to their environment, very different 

 from those living where light abounds. One form has phos- 

 phorescent light at the tips of its tentacles, another has a 

 protruding eye-like organ which glows at the end, furnishing 

 a light which it can direct at will over a wide field. Eyes 

 show a gradual change in various forms at different depths, 

 and they are absent in many deep sea animals. 



The light which enables the animals to see at great depths 

 is undoubtedly phosphorescent. This source of illumination is 

 common at the ocean's surface, as you must have observed fre- 

 C[uently on your own sea-coast. In mid-ocean the waves in the 

 wake of a moving vessel exhibit it brilliantly at iiight. We 

 were frequently able to read fine print by its aid alone on the 

 deck of the Challenger, fifteen feet above the water. 



My own views, I must admit, have not been fully accepted 

 by all geologists, but I am well eonviuced that the former gen- 

 ei-al belief that limestones are mainly detrital will not hold for 

 the deposits in mid-ocean. I strongly incline to the opinion 

 that all true limestones not made up of cemented aggregates 

 of shells, have passed through living organisms. In the deep 

 sea, the animals work over the mud. extracting the organic 

 matter and rejecting the limy fragments of shells. Coral build- 



