20 MORTALITY OF FISHES, WEST COAST OF FLOEIDA. 



seismic disturbance of low intensity might cause accumulated sedi- 

 ments to slide off into abyssal water, similarly releasing occluded 

 gases and also mixing up the mud with the water. It is known that 

 microseisms (as Prof. Woodworth terms them) are radiated from 

 this locality, and it is believed by some that they are due to the West 

 Indian cyclonic storms. 



This seems to be the most promising hypothesis. It might be ex- 

 pected that the water flowing JTito this region carries a large amount 

 of organic matter leached from the abundant Florida vegetation and 

 held in colloidal solution; that this organic matter, on striking sea 

 water heavily charged with lime is flocculated and falls to the bottom 

 on the uncommonly wdde expanse of continental shelf in this region ; 

 that as it accumulates on the bottom it decays anaerobically, yielding 

 methane, hydrogen sulphide, possibly carbon monoxide, and other 

 gases; that these gases, as generated, are confined by the pressure, in- 

 creasing sediment, and, perhaps by the limestone crust which appears 

 to cover the bottom-; that an earthquake shock, even an unnoticeably 

 mild one, would so disturb the sediment, or break the crust, as to 

 release the occluded gases, and that these gases work, by various 

 physiological and chemical means, the injury to fishes. These organic 

 gases, being rare in sea water, w-ould never be detected by the ordi- 

 nary analyses. 



The work of Prof. J. P. McClendon at Tortugas, in the summer of 

 1916, suggests that the marginal supply of oxygen in this region is 

 not great. In a letter on the subject he says: 



I think probably lack of oxygen killed the fish. When the Ph of tropical sea 

 water reaches about 7.5 there is no oxygen left in the water. At Tortugas the 

 Ph was about S.15 and there was about 4 cc. of oxygen per liter. 



It would, of course, be necessary to explain any deficiency of 

 oxygen. 



ALKALINITY AND SAL ilTY OF THE WATER. 



These two determinations were made as being most likely to reveal 

 any unusual condition of the water. The alkalinity is somcAvhat 

 higher than that of pure sea water. Dole found this to vary between 

 0.00237 N and 0.00257 N; McClendon found the alkalinity at Tor- 

 tugas in 1916 to lie between 0.0023 N and 0.0025 N, while the samples 

 taken in the region under discussion had an alkalinity varying from 

 0.00236 X to 0.00297 N. This may be explained by the large amount 

 of fresh water flowing into the salt water in this region, which is 

 generally rather strongly alkaline. The salinity is lower than that 

 of pure sea water; this is likewise explained by the fresh water 

 flowing in. 



