316 Doubts Relative to the Epochal and 



the eruptive rocks are in origin above and not below granite, 

 which is the generally received opinion. 



But if it be granted that the eruptive rocks are BELOW 

 granite, yet their extent is too limited, and the TIME of their 

 disruption in the order of stratification too recent, to admit 

 them as agents that can have supplied much of the material 

 for lime and magnesian limestone found in the sedimentary 

 rocks, from the gneiss system to those of the cretaceous or 

 tertiary formations. 



Hence the eruptive rocks, as agents in supplying lime to 

 the sedimentary ones, are insufficient, whilst their origin is 

 hidden in much obscurity. 



Having examined the origin of lime as derived from 

 granite upon the detrital theory, and found it wanting, it is 

 not unfair to inquire how the case stands as regards the 

 POTASH in both felspar and mica. As both these components 

 of granite contain much more potash than lime say five of 

 potash to one of lime we ought, by the process of 

 mechanical disintegration, to have for every foot in thickness 

 in lime, about five feet of potash. And if, in addition, the 

 laws of solubility are to be taken into account, then, as potash 

 and soda are much more soluble than lime or magnesia, the 

 excess of potash over lime ought to be greater still ; and 

 instead of being i to 5, it ought to be nearer i to 8. But 

 what is the fact ? In the whole geological series of stratifi- 

 cation, there is not one single potash stratum, only given 

 beds, like to common salt. 



Now, water disintegrates felspar, and with it the 

 contained potash, as most engineers connected with water- 

 works will decidedly affirm. And upon this subject Graham 

 thus speaks : " A comparison of compact and disintegrated 

 felspar shows that by the solvent action of water, the latter 

 has been deprived of half its silica, and above three-fourths 

 of the potash."* Hence the non-appearance of potash as the 

 * Graham's " Elements of Chemistry," ist edition, page 522. 



