"
_Petrosilex, &c._--"By the way, I received from Dr. Torrey a curious
mixture of petrosilex and prehnite in radiating crystals, which was sent
him by you, and collected at the West. He did not tell me the name, but
examination showed me what it was."
_Tufa from Western New York_.--"To day, a Quaker from Sempronius, New
York, has shown me some fine tufa. I mention it, because you may, in
your travels, be able to see it. He says it covers an acre or more to a
great depth, is burned into excellent lime with great ease, and is very
valuable, as no good limestone is found near them. Some of it is very
soft, like agaric mineral, and would be so called, were it not
associated with beautiful tufa of a harder kind."
_Geology of America_.--"You have explored in fine situations, to extend
the knowledge of the geology of our country, and have made great
discoveries. I congratulate you on what you have been able to do; I hope
you may be able, if you wish it, to add still more to our knowledge."
_Jan.
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