This valuable book is published by the Secretary of the American Iron-Association, and by authority of the same. This Association--now four years old--is not a common trades-union, nor any impotent combination to resist the law of supply and demand. Its general objects, as stated in the constitution, are "to procure regularly the statistics of the trade, both at home and abroad; to provide for the mutual interchange of information and experience, both scientific and practical; to collect and preserve all works relating to iron, and to form a complete cabinet of ores, limestones, and coals; to encourage the formation of such schools as are designed to give the young iron-master a proper and thorough scientific training, preparatory to engaging in practical operations." In pursuance of this wise and liberal policy, the Association has now published this "Iron-Manufacturer's Guide," containing, first, a descriptive catalogue of all the furnaces, forges, and rolling-mills of the United States and Canada; secondly, a discussion of the physical and chemical properties of iron, and its combinations with other elements; thirdly, a complete survey of the geological position, chemical, physical, or mechanical properties, and geographical distribution of the ores of iron in the United States. The directory to the iron-works of the United States and Canada enumerates 1545 works of various kinds, of which 386 are now abandoned; 560 blast-furnaces, 389 forges, and 210 rolling-mills are now in operation; and the directory states the position, capacity, and prominent characteristics of each furnace, forge, or mill, the names of the owners or agents, and, in many cases, the date of the construction of the works, and their annual production. The great importance of the iron-manufacture, as a branch of industry, in this country, is clearly demonstrated by this very complete catalogue. It shows that in the year 1856 there were nearly twelve hundred active iron-factories in the United States, and that they produced about eight hundred and fifty thousand tons of iron, worth fifty millions of dollars. When we consider that the greater part of the iron thus produced is left in a rough and crude state, merely extracted from its ores and made ready for the use of the blacksmith, the machinist, and the engineer,--when we remember that human labor multiplies by hundreds and by thousands the value of the raw material, that a bar of iron which costs five dollars will make three thousand dollars' worth of penknife-blades and two hundred and fifty thousand dollars' worth of watch-springs, we begin to understand the importance of the iron-manufacture, as an element of national wealth, independence, and power.