from Ochoa. Their outlets must therefore be closed by embankments; and the foot-hills, wherever their crests. fall below the contour 114, must be raised to that level. The main embankments will have to sustain a water pressure of about 60 feet, the level of the valleys being about 46 feet above the sea. Six embankments will have an aggregate base length of 3,440 feet, and along the crest of 13,685 feet. These closing gaps in the chains vary considerably in height, many of them being wholly above the ordinary water level in the basin-i e., from 1 to 8 feet high-while other gaps require embankments of much greater height. They are sixty-one in number, with a total length on the crest of 17,835 feet. Several important advantages are gained by this treatment.' The total length of basin created is 11.267 miles, 1 Major Dutton says: "These valleys are very numerous and intricate. But it is essential to note here as a highly important fact that none of them on the north side of the river have large drainage basins; but all, with a single exception, drain directly to the river in numberless. small streams, without uniting their waters to form considerable rivers. The exception is the San Francisco basin, whose waters drain into the San Juan; but even this tributary has a comparatively small watershed. Mr. Menocal proposed to solve all difficulties of this kind by converting a great part of the San Francisco drainage basin into a lake at summit level by means of embankments. The first reconnaissances seem to indicate a fortunate fitness in the topography of the basin for this project, and subsequent careful and systematic surveys have confirmed and established that impression. The project carried with it the necessity of opening a profound cut in the eastern rim of the San Francisco basin, which has received the name of the 'divide cut.' This is a work of vast magnitude and corresponding expense. But it has the merit of affording a complete solution of all other engineering difficulties, and of which 8.697 miles will have a water depth varying from 30 to 60 feet. In other words, of the 12 miles from the bank of the river San Juan to the deep cut to the eastward of this section, but 1233 miles will be wholly, and 2'570 miles partly, in excavation. The economy, however, is not confined to the saving in excavation, against which must, of course, be charged the cost of the embankments, but consists principally in the enormous saving in the deep rock excavation, and in the valley of the Deseado beyond, by carrying the summit level through into the valley of the stream. The increased cost resulting from the adoption of a much lower level would have been so great as to seriously handicap the undertaking financially. The gain in facilities of navigating and maintaining the canal is also important, for through wide and deep basins vessels can move at full speed, lie at anchor, or pass each other at all points, while in the restricted channel the position and speed of ships must conform to rigid regulations. At one time it was intended to utilize the whole length of the San Juan river from the lake to the Atlantic. But it was found, that while the river can be effectively utilized and handled from the point where it leaves the lake to the proposed junction of the canal with the river at the Ochoa dam, below that the river would be very difficult to deal with.1 insuring the permanence of the entire line against the destructive action of natural forces." Mr. Menocal says:-"A low level route from Ochoa to the Atlantic would be longer by about 12 miles, and wholly in excavation. On account of the shifting character of the channels, and the large amount of silt precipitated into the river by the San Carlos stream, it would be almost impossible to utilize the river on this portion as a channel, and even then it is very doubtful whether permanency could be obtained. I have met engineers in the United States In order to avoid the high ridges and projecting spurs, it must keep close to the banks of, and be but a little elevated above, the San Juan. The canal would therefore be in constant danger of destruction,—on the south by the river floods, and on the north by the accumulated drainage of an extensive watershed, presenting at all points complicated engineering problems of most difficult solution. By the high-level plan, the largest portion of that watershed is eliminated; and, of the balance yet affecting the canal, a large area is converted into extensive reservoirs, from which the surplus waters can, without difficulty, be discharged over waste weirs on the confining ridges into the low valley on the south, and through the numerous watercourses traversing the same into the San Juan." Major Dutton says:-"In searching for a route from this critical point to the sea, the earlier surveys disclosed clearly the fact that the southern side of the lower San Juan was impracticable, (1) by reason of the great amount of excavation required; (2) by reason of the many sharp turns, embarrassing to vessels of great size; (3) by reason of the gigantic cost of opening and maintaining a harbour; and 4th and most conclusive of all, the certainty of speedy breaches of the canal by the overwhelming floods of lateral tributaries which the line of the canal must cross. The north side of the river alone offered promises of feasibility. The doubtful feature was the San Francisco river. This stream drains an area on the north side of the San Juan which, in an ordinary country, would not be regarded as large, but which, in view of the excessive rainfall of this locality, was sufficiently large to be very menacing. In dry weather the stream is navigable only by small skiffs; in wet weather it is a powerful stream. It would be extremely dangerous to a location near the river and parallel to it. Such a location, moreover, would involve very formidable excavations and conservative works for a considerable distance below the San Carlos." D who have maintained the entire feasibility of utilizing the river throughout. But I am of opinion, from what I have seen of similar problems in various parts of the world, but more especially in tropical countries, where all the conditions were similar, that engineering skill, at any reasonable cost, could not control the lower 'section of the San Juan river through its reaches of sandy flats below the line of the foot-hills. The adoption of the particular line chosen by Mr. Menocal is not only much shorter and less costly, it is necessary for the safety of the canal. THE WESTERN SECTION. While the isthmus separating the lake from the Pacific is, at its narrowest point (where is found the very lowest depression in the whole Cordillera), not more than 12 miles in width, the most economical route connecting the lake shore with Brito has a length of 17:04 miles. It starts from the mouth of the Lajas, a small stream draining a limited watershed to the south of the line, and trends south-westerly through a broad valley slightly rising towards the "Divide," which it reaches at a distance of 4'70 miles from the lake. Descending thence on the Pacific Slope, at the rate of about 9 feet per mile, at a further distance of 1 miles it falls into the narrow, tortuous valley of the Grande, a waterless creek during the dry season, but a stream of considerable flow in the rainy portion of the year. Its maximum volume has been estimated as high as 10,000 cubic feet per second; but this is attained only in times of extra |