Geology. ; 135 
sion of sands, clays and marls, (consisting of silica, silicates of alumina, 
carbonates of lime, magnesia and oxyd of iron, derived by chemical 
rocks, once formed, are liable to alteration only by local and superficial 
agencies, and are not, like the tissues of a living organism, subject to 
incessant transformations, the pseudomorphism of Bischuf and Dana. As 
yet, Mr. Hunt is the only one who has attempted a rational explanation, 
strata into crystalline rocks, and his views, whether true or false, are to 
be judged by themselves, and not by comparison with those of Bischof 
or any other writer. Among the geologists who since the time of Hutton, 
have best comprehended the nature of the problem of rock metamorphism, 
are Boué, Virlet and Delanoué. We hope at an early day to discuss in 
the pages of this Journal, the question of mineral pseudomorphism, as 
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combination, by which they are converted into silicates of high specific 
gravity, such as pyroxene, garnet, epidote, chloritoid and chiastolite. In 
18 Way, as remarked by Mr. Hunt in his lectures before the Smithsonian 
