Frorn the Chicago Tribune. We havo given believers in the advisability of digging a ship-canal across Michigan, froui the mouth of the Kalaniazou River to soine point on the Detroit Iliver or Luke Erie, n fair showing, by printiug a numbor ut letters iu support of the project. It would no doubt be a marked advantage to have a broad and navigable water-course straight across the península between Lakes Michigan and Erie. If the inhabitauts of that soction had created the State, they would doubtless have arranged to bring thia about. All that would bo noeded is the erection of a couple of parallel ranges of huls and the subsidence of part of the valloy between them. But as nature ilid not cause this and man cannot, the only way to make the iuiproveinout now is to dain the rivera and dig a deep ditch clear across the península. The ditch would have to bo doep enough to float ships carrying from 1,000 to 1,200 tonB of freight, tor as soon as the iuiprovenii'iits on the Weiland Canal are finished the trado of our groat inland seas will be carried on in vessels of thal burden. This would require a clear depth of at least 14 feet. The ditch should bo large enough to allow two large vessels to pass each other. If only turn-outs were provided, the delay anc consequent exponse would be increa'sed At least a dozen locks on each side o: the Kumniit would have to be built These, as well as all the rest of the work would have to be constructed in the most substantial manner possible, for tugs would necessarily be employed in drawing the vessols through from lake to lake, a distance of some 200 miles and the wash from their paddies woulc speedily destroy anything but stone walls on the canal part of the route After the canal and slack-water par had been constructed in this costl; fasbion, in all the necessary length, breadth, depth, and thoroughness, it would be in constant danger of running dry, especially in the very season, midsummor, when it would naturally be most needed and used. The puddles, which are known as "lakes" along the projected course would be hard taxed at any time to keep the great ditch full, and could not do so when the heat of suinmer was sucking their waters into the earth and evaporating it into the air. We will, however, suppose that the needed amount of water could be got on the upper levéis in the dry season. Would the canal pay ? The yearly revenue would have to pay interest on the cost of construction and meet the running expenses, including the hoavy repairs which every canal constantly needs. The only source of income would be tolls. If these were high they would defeat their own object by preventing the use of the long and not straight ditch. If they were low, a certain number of ships would pass through the canal, bu.t we fear nothing like the number necessary to raake the investment a profitable one. The extra expenses of towago for so great a distance and the slowness of the navigation and inevitable delay would make many, perhaps most, captains prefer the broad open lakes, where they could go from 8 to 10 miles an hour by steam and pay no tolls to anybody, to where they could be towed only 2 or 3 miles an hour and pay for both this and the privilege of using the artificial oourse. Not a day would be added to the season of navigation. The narrow, shallow, still sheet of water in the canal would be frozen before the Straits were closed. The lake season always exceeds by weeks that on the Erie Canal. Probably, too, the cost of transportation would not be decreased a penny - perhaps increased. There inight possibly be a eoanty saving of time in the passage, but this would be more than counterbalanced by the extra expenses and dangers alroady catalogued. How, indeed, under any circumstances, could grain be carried from Chicago to Buffalo for less than the water rates of the past two years- 2 to 4 cents per bushei ? One point remains. Where is the money to come from ? This is no time to ask for subsidies from a nation already taxed almost beyond endurance. No subsidy could be got at Washington unless this scheme were joined with a number of otherg even more impracticable in an " omnibus bill," and the whole thing was then carried through by active log-rolling. This would involve in the end hundreds of millions, and add the same to the National debt. The State of Michigan will not build the canal. No State in the Union could afford to enter into such a dubious speculation. The only reasonable resource is private oapital. Who will f urnish it P It is not necessary to proceed a step farther in the discussion until that question is answercd.