The grandest canal in Spain for water supply is the “Canal of Isabel II.” It furnishes the supply for Madrid. It is built after the system of the ancient Romans—that is, aqueducts constructed in masonry arched over. Its total length is 45 miles. It has besides, thirty-one tunnels, partly cut straight through rocks which the canal traverses, and partly side-cut tunnels (one is five-eighths of a mile long) for obtaining water. At the present time, when the question of supplying London and other important cities with water is much agitated, it may be well to mention that by means of this canal 200,000 cubic metres of water, or 600 litres (a litre is about a quart) per inhabitant are brought to Madrid daily. Of these 600 litres 100 per head is for domestic use, and 500 for irrigating the districts adjoining Madrid. The quality of the water is said to be excellent; indeed it is alleged that if the air which it contains were abstracted it might be considered as distilled water. The pressure of the water in the conduits is almost without exception sufficient to raise it to the upper stories of the highest houses in Madrid. In some quarters of the city it could rise 75 yards above them. There are two road tunnels in Spain, one on the road between Grenada and Motril, 300 metres long, and one on the Pyrennean road between Barbastro and Benasquez, the length of which is 90 metres. Spain, for a country with a population under 16,000,000, cannot be said to be badly off for means of communication. The total length of roads in the kingdom on the 1st of January, 1867, was 4,137,640 miles of the first class, 3,265,700 of the second, and 1,908,112 of the third. About 2,800,000 are in course of construction. It is intended eventually to extend the road system of Spain to a total of about 22,500,000 miles. As already mentioned, the total length of Spanish railways on the 1st of January, 1867, was 3,182 miles. There are few tunnels of any length in the United States. The Cincinnati Tunnel is 3,337 yards long; the Kingwood 1,366. The Alleghany mountains are perforated by one, the property of the Pennsylvania Railroad Company, which is 1,204 yards long, 24 feet wide, and 22 feet high. There are four through the Blue Ridge Mountains, Virginia, the longest of which is 1,955 yards, the next 1,418 yards, with an uniform gradient of 1 in 70. The Long Duck Tunnel, New Jersey, is 1,437 yards in length. But the Hoosac Tunnel, Massachusetts, will, when completed, be the longest railway tunnel in existence—except the tunnel of the Alps—8,166 yards; it was commenced in 1855, but it has only been vigorously proceeded with since 1864; its total estimated cost is to be £1,100,000, of which about £420,000 have been expended upon the 2,350 yards already constructed; its width is 26 feet, height 24 feet; the rock through which it is pierced is mica slate mixed with a little quartz.[132]