1874.] 303 [Hunt. 



even less, would suffice to cause the ready precipitation of the clay 

 from the water. 



The first notice of the geological significance of this fact occurs, so 

 far as I am aware, in the Report of Messrs. Humphreys and Abbot 

 on the Physics and Hydraulics of the Mississippi, published in 

 1861, where, in the Appendix A, page xi., Mr. Sidell, having exam- 

 ined the turbid waters of the river near its mouth, found it to con- 

 tain about one two-thousandth of suspended matter, chiefly clay, 

 which required from ten to fourteen days to subside. He, however, 

 observed that the addition to it of a portion of sea-water, or of com- 

 mon salt, alum, sulphate of magnesia or sulphuric acid, sufficed to 

 render the turbid water clear in from twelve to eighteen hours. He 

 thus explained the ready precipitation of the suspended clay when 

 these turbid waters come in contact with the salt waters of the Gulf, 

 causing great deposits of fine mud, and helping us to understand the 

 origin of the accumulations of argillites and clay slates which are met 

 with in various geological formations. This action of salt water has 

 lately been insisted upon by an English author, who is apparently not 

 aware of the observations and conclusions of Mr. Sidell. The latter, 

 who does not appear to have followed farther this curious phenomenon 

 suggests that it may be explained by some action of the salts upon a 

 portion of dissolved organic matter, the coagulation of which may 

 precipitate the suspended clay; but experiments show that it is inde- 

 pendent of the presence of organic substances. 



An explanation is, however, I think to be found in the researches 

 of Guthrie on the formation of Drops, published in the Proceedings 

 of the Royal Society for 1864 (Vol. xiv). In studying the size of 

 drops of water falling from a small sphere of ivory, he found that the 

 cohesion of the water was diminished when it held saline matters in 

 solution, as was shown by the smaller size of the drops. This was 

 verified by experiments with solutions of various strengths of nitre 

 and of chlorid of calcium. It was found that the addition of eight 

 parts of the latter salt to one thousand of water, reduced by one- 

 ninth the size of the drops, as determined by their lessened weight. 

 These results show a diminished cohesion of the liquid to the ivory 

 sphere, from which it was by the force of gravity made to fall. The 

 cohesion, in virtue of which the extremely attenuated particles of 

 clay are held suspended in water in opposition to gravity, is, in like 

 manner, so far reduced by the addition to the water of a portion of 

 saline matter, that gravity and cohesion rapidly assert themselves 



