In the neighborhood of Dixon, a class of emigrants have established themselves, more opulent and more luxurious in their tastes than most of the settlers of the western country. Some of these have built elegant mansions on the left bank of the river, amidst the noble trees which seem to have grown up for that very purpose. Indeed, when I looked at them, I could hardly persuade myself that they had not been planted to overshadow older habitations. From the door of one of these dwellings I surveyed a prospect of exceeding beauty. The windings of the river allowed us a sight of its waters and its beautifully diversified banks to a great distance each way, and in one direction a high prairie region was seen above the woods that fringed the course of this river, of a lighter green than they, and touched with the golden light of the setting sun. I am told that the character of Rock River is, throughout its course, much as I have described it in the neighborhood of Dixon, that its banks are high and free from marshes, and its waters rapid and clear, from its source in Wisconsin to where it enters the Mississippi amidst rocky islands. What should make its shores unhealthy I can not see, yet they who inhabit them are much subject to intermittent fevers. They tell you very quietly that every body who comes to live there must take a seasoning. I suppose that when this country becomes settled this will no longer be the case. Rock River is not much subject to inundations, nor do its waters become very low in summer. A project is on foot, I am told, to navigate it with steam-vessels of a light draught.