I think it must be zinc."
_March 18th_.--Mr. Amos Eaton writes from Troy: "A second edition of my
_Index to Geology_ is in the press--about thirty-six pages struck off. I
have written the whole over anew, and extended it to about two hundred
and fifty pages 12mo. I have taken great pains to collect facts, in this
district, during the two years since my first edition was published. But
I am rather deficient in my knowledge of secondary and alluvial
formations; I wish to trouble you with a few inquiries upon
that subject.
"From what knowledge I have been able to obtain in that department, I am
inclined to arrange the secondary class thus:--
"Breccia: compact, or shell limestone; gypsum, secondary sandstone.
"I leave much, also, for peculiar local formations.
"A gentleman presented specimens to the Troy Lyceum, from Illinois, of
gypsum and secondary sandstone, and informed me that the latter overlaid
the former in regular structure. Myron Holly, and others, have given me
similar specimens, which they represent as being similarly situated,
from several localities in the western part of this State.
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