HOW THE EARTH WAS EXPLORED IN 1876. 555 



the land was found to be carried out into the sea some hundreds of 

 miles, and clays were being formed, mixed up with the dkbris of ani- 

 mals. Within a certain distance of the land the deposits, to a great 

 extent, were formed of this material. Over a great part of the North 

 Atlantic there is being deposited the Globigerina ooze composed, 

 principally, of small chambered shells, extremely minute; and these 

 shells were found in enormous quantities. This deposit is almost 

 entirely of carbonate of lime, and the only rock it could form would 

 be limestone; therefore, over a large part of the North Atlantic, and 

 over many other parts of the world, this limestone is being laid 

 down." These creatures live at and near the surface, and thence the 

 whole of this sort of material at the bottom is derived. "It might be 

 supposed that this formation ought to be as universal as is the distri- 

 bution of these animals on the surface. Singularly enough, this is not 

 the case. At the depth of 12,000 feet the shells become rotten and 

 yellow; at 13,000 feet there are no shells, and the bottom is one of 

 homogeneous red mud, which, instead of consisting of carbonate of 

 lime, is ordinary clay. I may here interpolate a fact to show how 

 abundant animal life is at or very near the surface of the ocean. The 

 steamer Great Eastern was lately in dock at Milford Haven for the 

 examination of her bottom, which had not been scraped since 1867. 

 Her bottom was found covered with an enormous multitude of mussels, 

 clustered together in one dense and continuous deposit, extending 

 over 52,000 square feet, and which, upon a calculation made, amounted 

 to not less than three hundred tons' weight, or enough to load with a 

 full cargo two ordinary collier brigs. 



" Another curious fact observed in the voyage of the Challenger 

 was, that all over the bottom of the sea there is a large quantity of 

 pumice, showing that there are volcanoes, either below the water or 

 otherwise, that are constantly throwing out material. This pumice, 

 which is the froth of lava, is frequently so light as to float on the water, 

 and wherever they were, in any part of the world, they saw it moved 

 about by the current over the surface of the sea. They found living 

 in the sea, on the surface, or just below, a great quantity of beautiful 

 organisms called Madiolarians. They increase with the depth, and 

 many occur at great depths that are not found on the surface at all. 

 The impression formed was that they lived all through the sea, and 

 down to the greatest depths. 



"The whole bottom of the Pacific, or the greater part of it, is red 

 clay. The temperature of the ocean at 13,000 feet is very low. It is 

 usually but a little above the freezing-point at the bottom of the Pa- 

 cific and the Atlantic, and portions of the Southern Sea. The general 

 temperature gradually falls from the surface until the depth of 13,000 

 feet, below which there is, throughout the sea, a uniform temperature 

 of 37 or 34, or a little below the freezing-point. The question arose, 

 Whence does the ocean derive this low and uniform temperature? It 



