178 C. Bar us — Viscosity of Solids. 



such as is distributed through the soil in the form of oxides or 

 carbonate. As this solution is exposed to the air or meets 

 with calcium carbonate, it will lose iron, the calcium carbonate 

 removing all free acid, and an excess of the latter rock will re- 

 move all iron from the solution, as ferrous carbonate, while the 

 manganese sulphate would remain in solution until exposed to 

 both air and calcium carbonate at the same time. Of course, 

 the deposition of either iron or manganese oxides from solu- 

 tions of sulphates by action of calcium carbonate results in the 

 formation of calcium sulphate, which is carried away in solu- 

 tion in the water ; so that the calcium is either wholly or in 

 part removed from the strata in which such deposits are 

 formed, and we would expect to find only occasional ledges 

 remaining as we find in the vicinity of the Orimora deposit. 



An additional argument for the transportation of manganese 

 as sulphate rather than bi-carbonate lies in the great depth at 

 which some deposits of manganese are found ; for the bi-car- 

 bonate would deposit oxide of manganese, wherever ex- 

 posed to the air, while the sulphate would, where calcium car- 

 bonate had been previously removed, need to penetrate to a 

 greater depth before reaching the conditions for its deposi- 

 tion. Moreover, the fact of the concentration of the manga- 

 nese in masses rather than its general distribution through the 

 decomposed shale would indicate that some condition addi- 

 tional to the exposure to oxygen had determined its deposition. 



It is also to be noted that after all sulphur is removed from 

 the overlying strata, the subsequent action of carbonated water 

 might then occasion some transfer and redistribution of the 

 previously formed deposits. 



University of Virginia, April 6th, 1888. 



Art. XIX. — MaxwelVs Theory of the Viscosity of Solids 

 and Certain Features of its Physical Verification;* by 

 Carl Barus. 



1. The viscosity of solids has been theoretically discussed in 

 the memoirs of O. E. Meyer, Boltzmann, Neesen, Warburg, 

 Maxwell, and Butcher. Yiews of a distinctly theoretical kind 

 have also been given by Weber and Kohlrausch, and more re- 

 cently by Nissen. In almost all cases, excepting alone Butch- 

 er'sf work, which formulates the theory of Maxwell,;); the 

 problem has been approached from distinct points of view. 



* Communicated by permission of the Director. This paper makes up a chap- 

 ter of a U. S. G-. S. Bulletin on the Viscosity of Solids, which will form the second 

 contribution to certain experiments on the Physical Constants of Rocks, following 

 a plan devised by Mr. Clarence King. 



f Butcher: Proc. Lond. Math. Soc, hi, 1878. 



X Maxwell: "Constitution of Bodies," Kncyclop. Brit.. 9th ed., p. 310, 1816. 



