186 Corresjjondence — Rev. 0. Fisher. 



These facts and comparative thicknesses are the basis of an 

 argument as to the local distribution of land and water in 

 Carboniferous times ; and it is shown that the peculiar change in 

 type which Carboniferous rocks undergo in passing from north to 

 south is due entirely to physiographical conditions, and not to any 

 theoretical assumption of contemporaneous faulting. It is shown, 

 moreover, that the Craven Faults per se have had nothing to do 

 with this change of type. The correlation of the limestone knolls 

 of Craven with the Pendleside Limestone is demonstrated to be no 

 longer tenable. 



ooiei2,ESi='ODNr3D:E32src:E. 



ME. A. E. HUNT ON THE AGE OF THE EAETH AND THE 

 SODIUM OF THE SEA. 



Sir, — In the volume of this Magazine for 1900 I reviewed 

 Professor Joly's theory, that the age of the earth can be calculated 

 by comparing the amount of sodium now in the sea with the time 

 rate at which rivers are at present conveying sodium down. Among 

 other matters I suggested that the salinity of rivers might be partly 

 due to sodium derived from sedimentary rocks, which had formerly 

 come from the sea. This would of course lengthen the computed 

 age of the earth. 



Mr. Hunt now suggests that "sea- water reached the heated rocks," 

 and he appears to consider that much of the sodium, which the 

 Dartmoor granites (at any rate) contain, was derived from the sea. 



This is turning Professor Joly's theory round about. Professor 

 Joly derives the salts of the sea from the igneous rocks. Mr. Hunt 

 derives the salts of the igneous rocks from the sea. 



My object in this letter is to direct attention to the difficulty of 

 explaining the undoubted abundance of water, which is extravasated 

 by volcanoes, to absorption from the ocean or from anj' other 

 external source. I have gone into my objections to this view 

 (whatever they may be worth) in my "Physics of the Earth's 

 Crust" (2nd ed., p. 144), where I have, in a note, given an account 

 of Daubree's experiment, to which Mr. Hunt refers. 



Since, alas ! my two friends have passed away, it may be 

 permissible to say, that I was on a visit to my dear friend Pro- 

 fessor Prestwich shortly after he had published his paper on " The 

 Agency of Water in Volcanic Eruptions," and Professor John Morris 

 was my fellow-guest. We two were talking about Prestwich's 

 theory that the volcanic water was derived ab extra, and that 

 water could enter into combination with molten rock. Morris said, 

 "Water would not be so foolish !" This was not a very scientific 

 reason, but it was putting his own idea pretty strongly. He also 

 told me that he had tried to dissuade Prestwich from publishing his 

 views of volcanic energj^, but without success. 



My own opinion is that water has been a constituent of the liquid 



