The physical nature of the country is well suited for carrying out such a project on a scale far larger than that required for sewage purposes, and works thus carried out would, to a small extent, restore the old water regime in this part of the continent. Before the vast surface changes produced during the last glacial period, three of the great lakes - Michigan, Huron and Superior - discharged their waters southward into the Gulf of Mexico by a broad river. The accumulation of glacial debris changed all this; the southern outlet was cut off, and a new one to the north was opened near where Detroit stands, making a channel to Lake Erie, which then became the outlet for the whole chain by way of Niagara. A very slight change in levels would serve to restore the present regime. Around Lake Michigan the land has been slightly raised, the summit above mean water level being only about 8 ft. Thirty miles from the south shore the lake level is again reached at a point near Lockport (see Fig. 2); the fall then becomes more marked. At Lake Joliet, 10 miles further, the fall is 77 ft.; and at La Salle, 100 miles from Chicago, the total fall reaches 146 feet. At La Salle the Illinois River is met, and this stream, after a course of 225 miles, enters the Missouri. In the whole distance the Illinois River has a fall of 29 ft. "It has a sluggish current; an oozy bed and bars, formed chiefly by tributaries, with natural depths of 2 ft. to 4 ft.; banks half way to high waters, and low bottoms, one to six miles wide, bounded by terraces, overflowed during high water from 4 ft. to 12 ft. deep, and intersected in dry seasons by lake, bayou, lagoon, and marsh, the wreck of a mighty past."

The rectification of the Illinois and the construction of a large canal from La Salle to Lake Michigan are, therefore, all that is necessary to open a waterway to the Gulf of Mexico, and to make Chicago doubly a port; on the one hand, for the enormous lake traffic now existing; on the other, for the trade that would be created in both directions, northward to Lake Michigan, and southward to the Gulf.

As a matter of fact this great scheme has long occupied the attention of the United States government. A bill in 1882 authorized surveys for "a canal from a point on the Illinois River, at or near the town of Hennepin, by the most practical route to the Mississippi River ... and a survey of the Illinois and Michigan Canal connecting the Illinois River with Chicago, and estimates from its enlargements." This scheme only contemplated navigation for boats up to 600 tons. In 1885 the Citizens' Association, of Chicago caused a report to be made for an extended plan. The name of Mr. L.E. Cooly, at that time municipal sanitary engineer, was closely associated with this report, as it is at the present time for the agitation for carrying out the works. This report recommended that "an ample channel be created from Chicago to the Illinois River, sufficient to carry away in a diluted state the sewage of a large population. That this channel may be enlarged by the State or national government to any requirement of navigation or water supply for the whole river, creating incidentally a great water power in the Desplaines valley." Following this report and that of a Drainage and Water Supply Commission, a bill was introduced into Congress supporting the recommendations that had been made, and providing the financial machinery for carrying it into execution.

Since that date much discussion has taken place, and some little action; meanwhile the sanitary requirements of the city are growing more urgent, and the pressure created from this cause will enforce some decision before long. Whether the new waterway is to be practically an open sewer or a ship canal remains yet to be seen, but it is tolerably certain that its dimensions and volume of water must approximate to the latter, if the large populations of other towns are to be satisfied. In fact the actual necessities are so great as regards sectional area of canal and flow of water - at least 600,000 ft. a minute - that comparatively small extra outlay would be needed to complete the ship canal.

The attention of engineers in Chicago, as well as of the United States government, is consequently closely directed at the present time to such a solution of the problem as shall secure to Chicago such a waterway as will dispose of the sewage question for very many years to come; that shall relieve the inhabitants on the line of the canal from all nuisances arising from the sewage disposal, and shall provide a navigable channel for vessels of deep draught. The maps, Figs. 1 and 2, give an idea of the most favored scheme - that of Mr. Cooley.

As will be seen, the canal commencing near the mouth of the Chicago River passes through a cut in the low ridge forming the summit level; then it runs to Lake Joliet, and through the valleys of the Desplaines and Illinois Rivers, to the Mississippi at Grafton, a distance of 325 miles. The elevations and distances of the principal points are as follows:

The project in contemplation provides that the depth of the canal as far as Lake Joliet (which is about six miles long) shall be not less than 22 ft., and on to La Salle not less than 14 ft. at first, with facilities to increase it to 22 ft. Beyond La Salle to the mouth of the Illinois, dredging and flushing by the large volume of water pouring in from Lake Michigan would make and maintain ultimately a similar depth.

As it appears recognized that the sewage channel of Chicago must be 15 ft. deep, and as provision is now being made all over the great lake system for vessels drawing 20 ft. of water, a comparatively small additional outlay would provide for a channel available for the largest lake vessels. It is claimed that by the co-operation of the Chicago municipality and the general government - the latter to advance a sum of not less than $50,000,000 - a ship (and sanitary) canal 22 ft. deep could be made from the lake to Joliet, extended thence to Utica, 20 ft. deep, and from there to the Mississippi, 14 ft. deep.

That such a work would vastly enhance the commerce, not only of Chicago, but of the whole section of the country through which the canal would pass, admits of but little doubt, and probably the outlay would be justified by results similar to those achieved with other great canal works and rectified rivers in the United States.

The following figures, showing the tonnage carried in 1888-89, give some idea of the volumes of water-borne traffic in America:

Except on the Mississippi, it may be reckoned that navigation is closed by ice during five months a year. It may be mentioned, by way of comparison, that the traffic on the Suez Canal during the year 1888-89 was 6,640,834 tons.

One very interesting point in connection with this work is the effect that the diversion of so large a body of water from the lakes will have upon their regime. At least 10,000 cubic feet a second would be taken from Lake Michigan and find its way into the Mississippi; this is approximately 4½ per cent. of the total amount that now passes through the St. Clair River and thence over Niagara.

The following table gives some particulars of the great lakes and the discharge from them:

The average variation in level of the lakes is from 18 in. to 24 in. during the year, and the range in evaporation from year to year is also very considerable; thus the evaporation per second on Huron and Michigan, as given in the table above, is nearly 67,000 ft., but the figures for another year show nearly 89,000 ft. per second, which would represent a difference of 6½ in. in water level. As a discharge of 10,000 cubic feet a second into the new canal would lower the level of these two lakes by 2.87 in. in a year, it follows that the difference between a year of maximum and one of minimum evaporation is more than twice as great as would be required for the canal, and even under the most unfavorable conditions the volume taken from the whole chain of lakes would not lower them an inch.

When the variations in level due to different causes - rain, wind, and evaporation being the chief - are taken into consideration, the effect of 10,000 cubic feet a second abstracted would probably not be noticeable. That this would be so is the opinion, after careful investigation, of many eminent American engineers. On the other hand there is a similar unanimity of opinion as to the advantages that would be obtained in the condition of the Mississippi by adding to it a tributary of such importance as the proposed canal. - Engineering.