2 Sir James Hall on the Consolidation of the Strata. 



himself friendly to the new doctrines, came forward to grapple 

 with one of the most formidable difficulties which were urged 

 against them. In the History of the Royal Society, Vol. iii. 

 p. 8. Edinburgh Transactions, there is given a short abstract 

 of two papers on the formation of granite. . It is to be regret- 

 ted, that these papers should not have been given at length. 

 The abstract, however, is sufficiently curious, and well de- 

 serving of the attention of any experimentalist, who may be 

 engaged in attempts to imitate nature in the formation of crys- 

 tallised rocks. We have only room for a short extract : — 



" In granites, which contain quartz and feldspar, it fre- 

 quently occurs, that the feldspar is seen with the form of its 

 crystals distinctly defined, whilst the quartz is a confused and 

 irregular mass, being almost universally moulded on the crys- 

 tals of feldspar. Now, were it true that all granite is formed 

 by fusion, the very contrary, it would seem, ought always to 

 take place, as feldspar is very easily melted, and quartz resists 

 the greatest efforts of heat that have hitherto been applied 

 to it. 



" The difficulty is thus obviated : It is well known, that 

 when quartz and feldspar are pounded and mixed together, 

 the mixture may, with difficulty, be melted and run into a 

 kind of glass, the feldspar serving as a flux to the quartz. 

 The same may be stated in another way, by considering the 

 feldspar, when melted, as a fluid, in which, as a menstruum, the 

 quartz is dissolved ; and in this view we may expect, by ana- 

 logy, that phenomena, similar to those of the solution of salt 

 in water, should take place. Now it is certain, that when ex- 

 cessive cold is applied to the salt water, the water is frozen to 

 the exclusion of the salt, the ice obtained yielding fresh water 

 when melted, and the salt, when the experiment is pushed to 

 the utmost, separating from it in the form of sand. Why 

 should not the same thing happen in the solution of quartz in 

 liquid feldspar, when the mass is allowed to cool below the 

 point of congelation of the menstruum? The feldspar may 

 crystallise separately from the quartz, as we have seen pure 

 ice formed separately from the salt ; in both cases, the conge- 

 lation of the. solvent being simultaneous to that of the dissolved 



