Professor Frederick Hall, of Middlebury College, addresses me (Jan. 14th) on the same subject.  He alludes to my treatise “On the Mines, Minerals, &c., of the western section of the United States;” a work for which our country and the world are deeply indebted to your enlightened enterprise and unrelaxing zeal.  Before reading it, I had a very inadequate conception of the actual extent and riches of the lead mines of the West.  It seems, according to your account, that these mines are an exhaustless source of wealth to the United States.  “I should feel glad to have them put under your superintendence; and to have you nurture up a race of expert mineralogists, and become a Werner among them.”

Professor Silliman writes (Jan. 25th):  “When I wrote you last, I had not been able to procure your memoir on the fossil tree.  I read it, however, immediately after, and was so much pleased with it, that I extracted the most important parts in the American Journal, giving credit, of course, to you and to the Geological Society.”

Jan. 29th.  Chester Dewy, Professor, &c., in Williams College, Mass., writes a most kind and friendly letter, in which he presents various subjects, in the great area of the West, visited by me.

Chalk Formation.—­“Mr. Jessup, of Philadelphia, told me that he believed you doubted respecting the chalk of Missouri, in which you found nodules of flints.  I wish to ask if this be fact.  From the situation, and characters and uses, you might easily be led into a mistake, for such a bed of any other earth would be far less to be expected, and be also a far greater curiosity.”

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. 29th.  Mr. McNabb says:  “I have just received a specimen of excellent pit-coal from Tioga county, Pennsylvania, near the head of the south branch of the Tioga River, and about twenty miles south from Painted Post, in Steuben County.  The quantity is said to be inexhaustible, and what renders it of still greater importance is, that arks and rafts descend from within four or five miles of the mines.”