There are many structures at present in existence bearing considerably greater loads than this, and the granite ashlar masonry of at least one, the Bear Valley dam in California, is subject to compressive stresses, reaching, when the reservoir is full, at least 40 to 50 tons per sq.
An hour, may weigh up to about 4000 tons, and loads of 2000 tons are common.
Given in 1905 by Professor Tornebohm to the Swedish parliament, credited the world with only io,000,000,000 tons of ore, and that, if the consumption of iron should continue to increase hereafter as it did between 1893 and 1906, this quantity would last only until 1946.
Above Spires, however, the river craft are comparatively small, but lower down vessels of 500 and 600 tons burden find no difficulty in plying.
In 1903 371,084,000 metric tons of goods, including animals, were conveyed by the German railways, yielding 68,085,000 sterling, and the number of passengers carried was 957,684,000, yielding 29,300,000.
A train weighing 92 tons could be drawn by one engine at the rate of 5 m.
The exportation of cornflour pastes sank, however, from 7100 tons to 350 between 1882 and 1902.
In 1919 the republic exported merchandise to the extent of 566 million tons and imported 183 millions.
Up to 1870 there was more anthracite mined in Pennsylvania than bituminous in the whole country, but since that year the production of the latter has become vastly the greater, the totals in 1907, in which year each stood at its maximum, being 83,268,754 and 332,573,944 tons respectively.
Deep, was opened in 1889, and the extensive improvements (including the York Dock, where vessels carrying 10,000 tons can discharge in four to six days) have been effected from time to time, making the harbour one of the most commodious in the United Kingdom.