The slave State which has increased _most_ rapidly to the square mile of all of them from 1790 to 1860, has had a smaller augmentation per square mile than that free State which has increased most _slowly_ per square mile during the same time of all the free States, and the result is the same as to wealth and education also. Under the _best_ circumstances for the slave States, and the _worst_ for the free States, this result proves the uniformity of the rule (like the great law of gravitation), knowing no exception to the effect of slavery, in depressing the progress of States in population, wealth, and education. Would we then in all these advance more rapidly, we must remove slavery and negroism, the retarding cause. I know it is asked, how shall we then cultivate the cotton lands of the South without slaves? This does not apply to the border States; but before closing these letters, I will prove conclusively, by the census and other statistics, what, from long residence in the South, and from having traversed every Southern State, I know to be true, that cotton is now raised there most extensively and profitably by non-slaveholders, and upon farms using exclusively white labor. Indeed the cotton raised on small farms in the South where there are no slaves and exclusively by free white labor, commands a price from five to ten per cent. greater than the slave grown cotton. In Texas, especially, it is a great truth, that skilled, educated, persevering, and energetic free labor, engaged voluntarily for wages or its own use, would, in time, when aided by improved culture and machinery, produce much larger crops and better cotton than now raised by the forced and ignorant labor of slaves, and at a much cheaper rate, at a far greater profit, than any crop now produced in the North, and in a more salubrious climate. In western Texas, counties on the same parallel with New Orleans, and a little north and south, cultivated mainly by Germans without slaves, produced large quantities of the best cotton, and the supply with augmented labor might be increased almost indefinitely. Having thrice visited Texas, and traversed nearly the whole State, north, south, east, and west, I speak from personal knowledge. In one county, I observed first rate wheat, cotton, and sugar cane growing in adjacent fields, and the soil and climate well adapted for all three crops. In Texas, the product of wheat has increased from 41.79 bushels in 1850, to 1,464,273 bushels in 1860, and the number of bales of cotton from 58,072 in 1850, to 405,100 bales in 1860, far exceeding the rate of increase in any other State. (See table of Census, No. 36, pp. 200, 210.) Having very nearly six times the area of New York, Texas, when cultivated by free labor, can produce cotton enough to clothe the people of the world, and supply all Europe with wheat also. The rapid colonization of Texas by freemen ought to add to our wealth, in this decade, a sum equal to the present debt of the United States, and terminate in our favor the effort to supplant us in the supply of cotton for the world.