512 



JSCIENOR 



[N. S. Vol. XI. No. 274. 



surface of the stones was dry, and they sunk immedi- 

 ately when it became wet by touching or by the move- 

 ment of the swell. 



" The slate fragments collected on the sea surface 

 had a specific gravity of 3.71. The specific gravity of 

 the water in the channel was only 1 .0049 at a tem- 

 perature of 15° C. (59° F.). The largest stone which I 

 obtained from the surface weighed 0. 8 gram . Twenty 

 of the smaller fragments had a mean weight of 0.3 

 gram. The fragments contained no air cavities per- 

 ceptible to the unaided eye." 



These stones, which are pictured in Nature, 

 are, it mast be confessed, extraordinarily large. 

 The specific gravity of the Llano sand was 2.59 

 and the largest grains could not approach the 

 stones above mentioned in size. 



To quote further from Nordenskiold : 



"On examining the floating stones one could dis- 

 cern small gaseous bubbles attached to the under sur- 

 face of them, and at the shore stones can be seen on 

 the very fringe of the beach which are just beginning 

 to float lightened by gaseous bubbles." 



In my paper (p. 31) a possible explanation is 

 offered for the presence of the ' gaseous bub- 

 bles ' : In one of my experiments I dug several 

 holes in the sand forming a bank in the bed of 

 the Llauo and when their sides caved in, the 

 dry grains forming the outer coat of the deposit, 

 were gently launched and floated much more 

 abundantly than in a previous experiment when 

 the surface was damp. Furthermore, as each 

 mass of sand slipped into the water, and ex- 

 clusive of the floating grains, sunk, the air con- 

 tained in the interstices between the particles 7-ose 

 to the surface forming a patch of foam or froth. 



Again Dr. Nordenskiold remarks : 



" It is probable that the stones were not only pro- 

 vided with gas bubbles, which can be perceived by 

 the eye, hut that they were surrounded by an envelope 

 of gas supported by an insignificant coating of algse, 

 of which the stones are surrounded. At least, traces 

 of diatoms and algje are discernible on the stones 

 after drying. The greasy surface of the mineral of 

 which the atones consisted also prevented the water 

 from adhering to them, and caused the stones to be 

 surrounded with a concave meniscus, which naturally 

 may have contributed to, and perhaps was the main 

 cause of their floating, which sometimes was further 

 facilitated by a patelliform shape of some of the 

 bigger stones." 



The floating sand of the Llano showed upon 

 careful examination no signs of the presence of 



low forms of vegetable growth, neither was it 

 in the least greasy. That the presence of oil 

 in a bituminous shale may facilitate its floating 

 property can scarcely be doubted. 



Nature for February 1, 1900 (p. 318), contains 

 two communications upon ' Floating Stones ' by 

 Messrs. Cecil Carus- Wilson and R. C. T. Evans, 

 respectively. 



Most of the points made by Mr. Carus- Wilson 

 are covered in the papers of Messrs. Graham, 

 Ladd and myself. It may, however, be of in- 

 terest here to call attention to the following. 

 He says : 



"The grains float as patches composed of fine and 

 coarse material clinging together ; the presence of the 

 very fine grains appears to facilitate the flotation of 

 the larger grains and shells." 



As bearing on this statement I will quote 

 briefly from my paper : 



"As I was sprinkling some sand upon the river for 

 experimental purposes, a pebble almost as large as the 

 end of my little finger fell into the center of a float- 

 ing patch, which, to my great astonishment and de- 

 light, was depressed, like a funnel, for, say, half an 

 inch before the cause of this unexpected phenomenon 

 broke through its surface and sunk to the bottom " 

 (p. 35). 



His statement regarding the formation of 

 ' patches ' had also been anticipated in my paper 

 (p. 36). 



Mr. Evans writes that he has observed the 

 phenomenon of floating stones at Kimmeridge, 

 where the flaky nature of the beach material 

 renders their appearance very common. 



In experimenting with broken roofing slate 

 he found that a small dried piece 1.5 X .75 cms. 

 by about 1 cm. floats easily on water when 

 gently placed on the surface. 



It will be seen from the above statements 

 that all observers agree that to float, the sand 

 or stones must be lightly launched without 

 complete wetting. 



Frederic W. Simonds. 



Univeesity op Texas. 



sea-bieds a sanitary necessity. 

 This country is on the verge of losing for- 

 ever one of the main features of its seacoast 

 charms — the sea-birds themselves. In fact, the 

 Terns, the most exquisite of the Gull family, 



