The Detroit mills manufacture excellent flour, and it is to be regretted that they are not capable of making a much larger quantity of their well-known brands. There are six flouring mills of different capacities in the city, and although they are generally at full work such is the demand for flour they make, that they are very often not able to supply their customers. These mills ought to be enlarged, or others built. Detroit, the commercial metropolis of a great wheat-growing State, should be capable of manufacturing an immense quantity of flour. The increased expenditure of money, in the purchase of wheat, would be very beneficial to the trade of the city. For the last fifteen years, the exports of breadstuffs from the United States have fluctuated very much. In 1846 they amounted to nearly twenty-eight millions of dollars, and rose in 1847 to sixty-nine millions. In 1848 they fell to thirty-seven, and in 1852 to twenty-six millions. In 1853 they amounted to nearly thirty-three millions, and in 1854 they rose to about sixty-millions, but fell in 1855 to about thirty-nine millions, and again rose in 1857 to seventy-seven millions. In 1858 they again declined to about fifty millions. We cannot accurately detail the exports of 1859, but they have been very light on account of fall in the European market, after the termination of the war in Italy. During these years there were various causes for the remarkable fluctuations which we have noted; namely, famine in Ireland, the Crimean war, and the failures of the harvest at home and abroad, nor have these exportations been regularly divided or spread over the various months of each year. They have increased or diminished according to the European demand, governed by the supply at home and regulated by advices from the other side of the Atlantic. It is likely that the export of breadstuffs in 1860 will be very considerable. Michigan possesses many advantages over her sister States, and these enable her to bear up against monetary panics better than they. Her immense length of lake coast is indented with excellent harbors, which invite commerce from every quarter, and furnish excellent outlets for her surplus produce or mineral wealth. The great and diversified resources of the State support her in the evil day, and bring her through a commercial crisis in safety. From the ushering in of the year to the close, there is not a day in which the marts of commerce are not enlivened by the contributions of grain or live stock from our fields, fish from our lakes, lumber from our forests, or ores of various kinds from our inexhaustible mines.