160 MARINE ANIMALS OF MASSACHUSETTS BAY. 



Aided by a friend, Captain Mc Andrew, who placed his yacht 

 at his disposal, he made a series of observations on the British, 

 Scandinavian, and Danish coasts, and explored also with the 

 same object the shores of the Mediterranean. Not content with 

 soimding the present ocean, he sunk his daring plummet in the 

 seas of past geological ages, and by comparing the nature and 

 position of their fossil remains with those of living marine faunae, 

 he measured the depths of the water along their shores. He col- 

 lected a vast amount of material, and the results of his labors 

 have formed the basis of all subsequent generalizations upon this 

 subject. Nevertheless he arrived at some erroneous conclusions, 

 which, had he lived, he would no doubt have been the first to 

 correct. Dredging from low-water-mark outward, he found that, 

 from the Laminarian and Coralline zone, the animals began grad- 

 ually to decrease in number, and that, at a depth of two or three 

 hundred fathoms, the dredge always came up nearly empty. 

 He inferred that at a certain depth the weight of water became 

 too great to be endured by animals, and that the ocean beyond 

 this line, like the land beyond the line of perpetual snow, was 

 barren of lifb. This result seemed the more probable on account 

 of the immense pressure to which animals are subjected, even at 

 a comparatively moderate depth. A column of water thirty-two 

 feet high is equal to one atmosphere in weight ; this pressure 

 being increased to the same amount for every thirty-two feet of 

 depth, it follows that a fish one hundred and twenty-eight feet, or 

 some twenty fathoms below the surface, is under the pressure of 

 almost four atmospheres plus that of the air outside. Wherever 

 tides run high, as in the Bay of Fundy, for instance, where an 

 animal is under the pressure of one atmosphere at low tide, and 

 of three atmospheres at high tide, we see that marine animals are 

 uninjured by great changes of pressure. Yet it seems natural to 

 suppose that there is a limit to this power of resistance ; and 

 that there must exist barren areas at the bottom of the ocean, as 

 destitute of life as the regions on the earth which are above the 

 line of perpetual snow. No doubt pressure does influence the 

 distribution of life in the ocean ; but it would seem, from subse- 

 quent observations, that the boundaries assigned by Forbes were 

 far too narrow, and that the structure of many marine animals 



