We are led naturally to ask, where the progress of our sea breezes will ultimately be stopped? No confidence can be placed in any answer to this question. If they should ever pass the mountainous country which separates the waters of the ocean from those of the Mississippi, there may be circumstances which might aid their further progress, as far as the Mississippi. That mountainous country commences about two hundred miles from the sea coast, and consists of successive ranges passing from northeast to southwest, and rising the one above the other to the Allegany Ridge, which is the highest of all. From that, lower and lower ridges succeed one another again, till having covered, in the whole, a breadth of two hundred miles from southeast to northwest, they subside into a plain, fertile country, extending four hundred miles to the Mississippi, and probably much further on the other side, towards the heads of the western waters. When this country shall become cultivated, it will, for the reasons before explained, draw to it winds from the east and west. In this case, should the sea breezes pass the intermediate mountains, they will rather be aided than opposed in their further progress to the Mississippi. There are circumstances, however, which render it possible that they may not be able to pass those intermediate mountains. 1. These mountains constitute the highest lands within the United States. The air on them must consequently be very cold and heavy, and have a tendency to flow both to the east and west. 2. Ranging across the current of the sea breezes, they are in themselves, so many successive barriers opposed to their progress. 3. The country they occupy is covered with trees, which assist to weaken and spend the force of the breezes. 4. It will remain so covered; a very small proportion of it being capable of culture. 5. The temperature of its air, then, will never be softened by culture. Whether in the plain country between the Mississippi and Allegany mountains, easterly or westerly winds prevail at present, I am not informed. I conjecture, however, that they must be westerly: and I think with you, Sir, that if those mountains were to subside into plain country, as their opposition to the westerly winds would then be removed, they would repress more powerfully those from the east, and of course would remove the line of equilibrium nearer to the sea coast for the present.