CIRCULATION OF AQUEOUS SOLUTIONS. 1021 



influence the result. For instance, it will be seen (pp. 1086-1087) that 

 calcium carbonate may be very influential in precipitating the sulphides 

 from aqueous solutions. It is supposed that the same reactions may take 

 place with dense gaseous solutions at high temperatures; indeed, it might 

 be argued that the calcium carbonate would be even more active with 

 gaseous solutions than with aqueous solutions. In this connection the very 

 frequent occurrence of the disseminated ores and deposits with irregular 

 boundaries, with garnet, pyroxene, tourmaline, and other heavy anhydrous 

 minerals as simultaneously developed g-angue minerals in limestone is to 

 be noted. (See pp. 1052-1056 ) 



CIRCULATION OF AQUEOUS SOLUTIONS. 



The general circulation of aqueous solutions is a function of the amount 

 of water in the rocks, of the form, continuity, size, and amount of the open- 

 ings in the rocks and of difference in head, difference in temperature, and 

 mechanical action. 



As to the amount of water in openings, in some cases the openings are 

 not full and in some they are full, or the rock is saturated. Where the 

 rocks are not saturated the chief forces producing circulation are gravity 

 and molecular attraction. Gravity tends always to carry the water down- 

 ward. Molecular attraction, or what is ordinarily called capillarit}, tends 

 to draw the water to places where the pore spaces have little water. It 

 therefore is an effective force only where the rocks are not saturated with 

 water. In the saturated rocks the forces producing movement are gravity, 

 heat, and mechanical action. Where the rocks are saturated hydrostatic 

 pressure is active, and therefore under these conditions flowage is usually 

 much more rapid than where the rocks are not saturated. The flowage is 

 also rapid in proportion as there is unequal head and unequal temperature 

 in the two columns. The movement of water caused by gravity is due to 

 the unequal weights of the columns of moving water. The unequal weight 

 may be due to difference in the lengths or in the temperatures of the vertical 

 columns or the two combined. That difference in length gives difference in 

 weight is obvious. Where two connected columns of water have unequal 

 temperature, the cooler column is the denser of the two, and therefore 

 under these circumstances gravity in connection with heat produces circu- 

 lation. In regions where the increment of heat is normal, there may be 



