Reviews, — Br. T. Sterry Hunt's Chemico- Geological Essays. 559 



to the second edition of his Essays, he expresses his belief that J. D. 

 Dana has abandoned his former opinions on metamorphism, though 

 not to the extent that might be desired. 



The essay on Granite and Granitic Veinstones (1871-1S72) is a 

 very useful contribution. Dr. Hunt's experiences are chiefly derived 

 from the Green and White Mountain Series, and from the Laurentians 

 in Canada and New York State. The distinction between granite 

 and gneiss must be made chiefly on geognostical grounds. As regards 

 granitic veins, the notion that all are the result of some process of injec- 

 tion is a general one, though the author has pointed out that some are 

 concretionary and of aqueous origin. He would call these rather 

 endogenous, to distinguish them from intrusive or exotic rocks (such 

 as granitic dykes) and from sedimentary or indigenous rocks. They 

 are in fact, according to this view, exfiltration veins, and vary from a 

 few inches (sometimes an isolated nodular mass almost like a geode) 

 to 60ft. or more. Such veins, to judge from numerous descriptions 

 given by him, often exhibit a banded structure with alternations of 

 minerals, as quartz and felspars (chiefly orthoclase), and frequently 

 contain fine crystals of different minerals, chiefly silicates. It is no 

 great strain upon our faith to believe in exfiltration as the origin of 

 hydrated silicates, as zeolites ; but to attribute to such quantities of 

 anhydrous silicates a concretionary origin is a bolder conception. 

 Yet it is evident to any one who has studied a veined gneiss in section 

 that there do occur geodic cavities and strings filled with bands of 

 quartz and felspar in large masses, which seem to be cut off and 

 isolated. The difficulty in these cases has always been to understand 

 how the apple got into the dumpling. At the same time Sterry Hunt 

 considers that, although there is a distinction between open veins and 

 geodes formed in cavities, the contents, whether in granitic rocks or 

 fossiliferous limestones, are not sensibly affected thereby. Such vein- 

 stones must consequently be looked upon as a kind of extract of the 

 rocks, due to hydrothermal action, the many varieties resulting from the 

 changing composition of the waters which circulate in the fissures, or 

 are diffused through the rock itself. 



It should be observed that in the Laurentians, the metalliferous 

 veins carrying galena, blende, pyrites, and chalcopyrite are more 

 recent than the veinstones just noticed, as the former cut the Pots- 

 dam sandstone, etc., whilst the latter group of veins are old enough 

 for the Potsdam sandstone to rest upon their eroded outcrops. This 

 fact may have an important bearing upon the origin of metalliferous 

 deposits ; a subject discussed, in the next essay, before a general 

 audience at New York, where he declared that, what the alchemists 

 sought for in vain — viz. the universal menstruum, is neither 

 more nor less than water aided by heat, pressure, and the presence 

 of certain substances. The metals, he had previously stated, 

 seem to have been originally brought to the surface in watery 

 solutions, were afterwards separated and reduced as sulphides, 

 and mingled with contemporaneous sediments, and were during 

 subsequent metamorphism redeposited in fissures in the metal- 

 liferous strata, or ascending to higher beds gave rise to metalli- 



