And if you consult Fremont’s map, printed by order of the Senate in 1848, you will find, near the source of one of the branches of the Gila River, “copper and gold mines” laid down. And if I am not greatly mistaken, it will turn out that the Mormons are in possession of the richest kind of mines, east of the Sierra Nevada. It is known, too, that silver and copper mines have, for many years, been worked in New Mexico; and I am informed by Hugh N. Smith, Esq., that there are, in that territory, gold, silver, copper, lead, and zinc mines of the richest quality, and that the reason why they have not latterly been worked more extensively is, that it is prevented by the incursions of the Indians. He is of the opinion, and he is borne out by what history we can get on the subject, that when these mines shall come to be explored, their wealth will turn out to be enormous. When you have once cast your eye over the country lying west of the Rocky Mountains, and east of the Sierra Nevada, and are informed of the peculiarity of the gold bearing region, you at once become convinced that the United States is in possession of mineral wealth so vast, that ages will not be able to measure its extent. And when these mines shall begin to be developed, and their unquestionable richness known, population will set that way, attended with the usual consequences, high prices, and a demand for labor. If slave labor is like other capital, if it will go where it is best paid, then we have a right to say it will seek these mines, and become a part of the producing capital of the country where those mines are located. That these whole regions are filled with rich mines, is little less than certain, and that they can be profitably worked by slave labor is sure. Hence, were I a southern man, and my property invested in slaves, I should consider the markets of New Mexico, Utah, and California, for slave labor, worthy of an honorable contest to secure. I am, sir, with due consideration, yours, truly, SAMUEL R. THURSTON. 5. The Kennebec letter has another most extraordinary and discreditable passage. It is near the close. Mr. Webster quotes from a speech delivered by him in the Senate, March 23, 1848, says it was published in newspapers and circulated in pamphlet form, and that that speech contained the same doctrines in regard to the “legal construction and effect of the resolutions” for admitting Texas, as are contained in the speech of the 7th of March. He says nobody complained then, and he wonders that any body should complain now.