JANESVILLE is the county-seat. It contains 3,500 inhabitants, and is rapidly growing. Rock river affords ample water-power, on which is already built several fine mills, and other machinery. The village occupies both sides of the river; and equals most towns in the state in activity of business. Mr. LAPHAM thus describes its admirable location in 1846:   "It is situated on a flat, or level, between the river and the foot of the bluffs, which are about one hundred feet high. The courthouse is erected on the bluff, giving it a very prominent appearance. Janesvffie is the point at which much of the trade between the eastern and western portions of the Territory crosses Rock river, and a bridge is now erected for its accommodation. The distance from Janesville to Milwaukee is sixty-five miles, and the same to Racine; giving the citizens a choice of two ports on Lake Michigan, reached in the same distance; it is 13 miles from Beloit, 41 from Madison, 31 from Monroe, and about 80 from Mineral Point."   A Railroad Company is chartered, the stock subscribed and the work commenced in good earnest, to run a line from Fon du lac to this place; thence, southeast through Walworth county into Illinois, and on to Chicago; which will be speedily constructed. Good building and limestone is quarried here in abundance.

Mr. Thompson's Letters. The following are extracts of letters, written in June and July last; in copying from these letters I have omitted what was not of general interest.   "JANESVILLE is already a town of considerable trade, one of those inland river towns that every State requires as a central depot. It has now one of the best hotels in the State and many fine stores. The ride from Janesville through Rock, Walworth, and Milwaukee counties, though it exhibited the riches of the country—'as good land as ever lay out doors'—was any thing but comfortable to a spare body already jolted by two days' staging. That Troy marsh and the corduroy make one ache for the completion of plankroads."