Julien.] 148 [December 6, 



tion, both in the veins and rock-masses, absolutely require, and 

 can be simply explained by the introduction of a solution of soda 

 and alumina into the fissures and interstices, during the period of 

 alteration and metamorphism. The combination of soda with 

 silicates of aluminum and iron, perhaps previously formed, has 

 produced all the minerals of the vein-series ; while the precipita- 

 tion of the alumina naturally ensued from the separation of its 

 alkaline solvent. The question then presents itself of the evidence 

 of the introduction of such a solution. This is found in the strata 

 of hornblende-gneiss, which everywhere surround the dunyte-beds, 

 and are abundantly traversed, all along the dunyte-belt, by the 

 huge veins of endogenous granyte, now largely exploited to supply 

 mica for commercial purposes. Into these there has certainly 

 been an introduction, by subterranean thermal solutions, of soda 

 and alumina, as shown both by the development of a long series 

 of crystallized mineral-silicates, containing those with other ele- 

 ments, and elsewhere even by the precipitation of corundum 

 itself (in association with muscovite, margarite and albite), in a 

 certain class of small veins in the gneiss, of limited occurrence 

 but great interest. 



It is a natural enquiry, whether there is any evidence of the 

 former occurrence of dunyte at other points along the Appala- 

 chian belt between North Carolina and Canada ? Of this I have no 

 doubt. The actinolytes, amphibolytes and hornblende-schists, as 

 well as many of the steatytes, talc-schists and serpentines, which 

 occur all along to the northward throughout these Montalban 

 rocks, are in many cases, I believe, the equivalents, usually more 

 crystalline, of their southern congeners. 



The question of the origin of the olivine in this concentrated 

 form has been met by three hypotheses : 



First, that the material is of an eruptive origin. 



Secondly, that it is a chemical precipitate. 



Thirdly, that it is a mechanical accumulation, in the form of 

 ancient olivine-sand. 



It has already been briefly indicated that both the petrographi- 

 cal and lithological phenomena observed present, in my opinion, 

 insurmountable objections to the first two hypotheses. It remains 

 then to suggest the source from which such olivine-sands have 

 been derived. Doubtless from some ancient terrane, perhaps of 



