In cotton-weaving, however, the unit of industry is growing, factories in 1870 numbering nine hundred and fifty-six; in 1890, nine hundred and five; in 1900, one thousand and fifty-five, the later increase being due to the fact that many new factories in the South have been started in the last decade. The population meantime doubled. This movement has been going on for seventy years, there being about the same number of mills in 1900 as in 1830, though population had multiplied six-fold. Iron- and steel-mills numbered one thousand three hundred in 1880, one thousand in 1890, and nine hundred and sixty-five in 1900. In industries having local markets and sources of supply for materials, the change has been less rapid. There were twenty-four thousand grist-mills in 1880, eighteen thousand in 1890, and twenty-five thousand in 1900, a change of ratio from two thousand one hundred to three thousand population per grist-mill. There were twenty-six thousand sawmills in 1880, twenty-two thousand in 1890, and thirty-three thousand in 1900, a change from about one thousand nine hundred and twenty to two thousand two hundred and seventy persons per sawmill. But while the number of establishments in these staple industries was decreasing, the number of employees per establishment in most cases was increasing. The average in all industries, in 1870, was eight; in 1890, twelve; in 1900, ten and four tenths. In cotton-mills, in 1870, the average was one hundred and eighty-four; in 1890, two hundred and forty-four; in 1900, two hundred and eighty-seven. The grist-mills, in 1880, had two and four tenths persons per establishment; in 1890, three and four tenths. The sawmills, in 1880, averaged six employees each; in 1890, fourteen; iron- and steel-mills in 1880, one hundred and twenty-one each; in 1890, one hundred and ninety-six. [Sidenote: Growing concentration of capital into large industries] 4. _The amount of capital per establishment is tending to increase in the leading lines of industry._ The amount of capital is not so easy to determine as the number of employees, and it is recognized that the census figures on this subject are only approximately correct. We are told that in cotton-mills, in 1830, the average capital invested was fifty thousand dollars; in 1890, nearly four hundred thousand dollars; in 1900, four hundred and forty thousand dollars. It is easy to observe the large increase in investment of capital in flouring-mills since the new processes came into use. The average capital of all industries does not grow as in the staple ones, for many smaller industries have come into existence. In 1880, the average capital was eleven thousand dollars; in 1900, it was eighteen thousand dollars. [Sidenote: Recent formation of combinations]