198 CARNEGIE INSTITUTION OF WASHINGTON. 



together. The rock is particularly free from carbonaceous matter or impuri- 

 ties of any kind, and so closel}'^ resembles the clean beach-sand as to be in- 

 distinguishable from it, except for the matter of cementation. On the other 

 hand, the bulk of the key sands is discolored by large amounts of carbonaceous 

 material. The "beach-rock" seems to occur only between high and low water 

 (maximum difference approximately 2.5 feet), and is so rapidly disintegrated 

 by the waves and marine organisms that it would soon cease to exist unless 

 covered and protected or 'periodically reproduced. Where the shape of the 

 beach is subject to change by wave and current action, no rock is formed. 

 In 1912 Dr. Vaughan observed that "beach-rock" is now exposed near the 

 landing-stage at Loggerhead Key, where once was a depth of several feet of 

 water, showing conclusively that the rock has been formed since the hurricane 

 of October 17, 1910, swept the shell-sand into place. 



By means of a pump and standpipe, the latter sunk some distance back 

 from the beach, I was able to prove that the shell-sand of the key was par- 

 ticularly porous to a depth of at least 14 feet (several feet below low tide- 

 level) and that the sea-water passes through the island to the extent that it is 

 even affected by the slight rise and fall of the tide.^ 



During a two days' heavy rain the water was found to stand considerably 

 higher in the standpipe. It is reasonable to suppose that in the case of an 

 exceedingly heavy rain, such as must take place during a tropical storm, the 

 key would rem^ain saturated with rain-water having an acidity approaching 

 Ph 4.75 before its contact with the sand. The acidity of the pure rain-water, 

 however, would be increased by the humus acid in the key sands, as the water 

 percolated through them.^ 



In case of very heavy rain, the key would act like a huge sponge, the ground- 

 water level being raised nearly, if not quite, to the surface. After a two days' 

 rain the water from the driven pipe was tested and found to contain just twice 

 as much CaCOs in solution, or colloidal form, as the sea-water. 



My theory is that after an exceptionally severe storm, during which fresh 

 sand is swept upon the beach in places and the beach itself scoured in others, 

 the bulk of the key sands above tide-water level are saturated with a strong 

 solution of calcium carbonate. This solution continues to trickle out through 

 the heach sands, at ground-water level, for several days, and upon exposure 

 to the air deposits calcimn carbonate in the spaces between the bits of shell, 

 thus forming the "beach rock." The precipitation of the CaCOs is probably 

 due to the relief of pressure, the escape of C02, and the consequent lowering 

 of the solubiHty of the CaCOs. The fact that the "beach rock" can not owe 

 its origin to the action of putrifying matter in place, such as seaweeds, etc., is, 

 I beheve, proved by the total absence of any carbonaceous material in the 

 rock itself. 



Researches on the Production of Light by Luminous Animals, by 

 E. Newton Harvey. 



My previous researches on light production in Cypridina, a luminous crus- 

 tacean, reported in the 1917-18 Year Book, led to the conclusion that luciferin, 

 the oxidizable material of Cypridina, is in all probability related to the pep- 

 tones, while luciferase, the catalyst in whose presence luciferin oxidizes with 



1 The supeiintendent of the Light-House Board, Mr. Putnam, assures me that he is unable 

 to find any record of the material encountered when the excavation was made for the founda- 

 tion of the light-house at Loggerhead Key. 



*The dissolving power of the humus acid is probably more highly effective than that of 

 pure rain-water alone. At any rate, both have a more solvent action upon the beach-sands 

 than ordinary sea-water. The Ph of normal sea-water is 8.2. The Ph of the "pipe water" 

 was found to be 7.85, the decrease in acidity being due to the dissolved CaCOs. Water with 

 a Ph higher than 7 will not dissolve limestone. 



