266 CHAMBERLIN— THE AGE OF THE EARTH. 



ter of these muddy waters contains a large part of the acid radicals 

 with which the basic radicals of the true solutions were united in the 

 parent rock and in the soils. While it is known that the muddy 

 waters contain hydrous silicates of alumina and iron, partly colloidal 

 and partly non-colloidal, together with finely divided siliceous silts 

 and colloidal silica, full and exact information is lacking. Dr. Collins 

 says that "the dissemination of silica in natural waters, particularly 

 turbid waters, is one of the least accurately known of the determina- 

 tions of substances present in appreciable quantities." -° He adds 

 that even " the exact state of the silica present in a perfectly clear 

 water is usually not known. It may be colloidal or it may be present 

 as a silicate radical." In addition to this — or perhaps the cause of 

 it — investigation is embarrassed at the inland end of the cycle by the 

 fleeting and irregular nature of the freshet stage, and by the rapid and 

 intricate changes within the soils. The changes in the soil are so 

 rapid in certain respects that F, H. King found it important to make 

 his determinations of water-soluble solutions by means of an impro- 

 vised laboratory in the field so that determinations might be made as 

 promptly as possible after the sample tube had taken the soil from its 

 natural relations.-^ At the sea end of the cycle the recombinations 

 of the acid radicals with the basic radicals seems to take place chiefly 

 at the base of the turbid water as it is carried out over the concen- 

 trated sea solutions and diffuses into them. Before the acid radicals 

 reach the bottom the reversing phase of the cycle has probably ended 

 and a new cycle begun under sub-oceanic conditions. The experi- 

 mental evidence in support of this conclusion is buried in a great 

 mass of literature which relates primarily to other elements, particu- 

 larly the elements that form plant foods, such as potassium, phos- 

 phorus, etc., and those that form precipitates such as calcium and 

 magnesium carbonates, but when these scattered data are gathered 

 together their combined import is sufficient to make clear the essen- 

 tials of what happens.^^ 



20 W. E. Collins, Chief of the Quality of Water Division, U. S. Geol. Surv. 

 Personal communication. 



21 Bull. 26, U. S. Dept. Agri. (1905). PP- 26-27. 



22 The following are among the more important early investigations : 



Way, Jour. Roy. Agri. Sac, Vol. 11 (1850), pp. 313-79; Vol. 13 (1852), 

 pp. 123-43; Vol. IS (1854), P- 491- 



