Railroad construction during the next decade to 1880 was extremely active. East of the Mississippi developments were confined in the main to building branches and feeders. One new through line in the East was opened, by the entrance of the Baltimore & Ohio into New York in 1873 and into Chicago in the following year. Another important enterprise was the building of the Air Line route to connect Atlanta with Richmond by a road traversing the fertile Piedmont belt. The completion by the state of Massachusetts of the Hoosac Tunnel line, providing a new outlet to the west from Boston, was also a notable achievement. This route was at last opened in 1874 after a painful experience extending over twenty years, involving an expenditure by the state of about $17,000,000. Most of the new railroad building of the seventies took place in the upper Mississippi valley. The states of Wisconsin, Minnesota, Iowa, (eastern) Nebraska and Kansas were rapidly gridironed with new lines. Much of this construction took place after 1868, activity culminating in 1871 with the building of no less than 7,379 miles of line. The panic of 1873 put an end to all this, except in California where expansion went on unabated. Nearly one thousand miles of new line were added to the systems of this state during the five years to 1878,--nearly doubling its mileage during this period. Elsewhere in the country little was accomplished during the protracted hard times. In 1875, for instance, only seventeen hundred miles were constructed. This cessation of development did not change for the better until the resumption of general prosperity in 1878. The net result of ten years building was, nevertheless, considerable, represented by an expansion from 53,000 to upwards of 93,000 miles of line. Railroad building, in fact, increased about two and one-half times as fast as population. So that by 1880 the United States was already more amply furnished with transportation mileage than any country in Europe. Among the important events to be associated with this period was the opening of the first transcontinental route, marked by the joining of the Union and Central Pacific railroads in 1869. The history of its construction under liberal land grants from the Federal government belongs in another place. Aside from the political effect, the economic results were immediate. Population at once flowed over onto the Pacific slope. And a large volume of trade was at once deflected from the sea route round Cape Horn. The value of goods shipped by water between New York and San Francisco, which in 1869 amounted to $70,000,000, fell in the next year to $18,600,000, and in 1872 to less than $10,000,000. The success of the enterprise, together with growing interest in the Pacific states, doubtless led to the opening of construction of the Northern Pacific as a transcontinental route in 1870.