Many of the circumstances accompanying this rapid expansion were novel and important. Beginning with a federal grant to the Illinois Central, for example, in the middle of the century, both the nation and the states assisted the roads by gifts of millions of acres of land. It was to the advantage of the companies to procure the grants on the best possible terms, and they exerted constant pressure upon congressmen whose votes and influence they desired. Frequently the agents of the roads were thoroughly unscrupulous, and such scandals as that connected with the Credit Mobilier were the result. More important still, the fact that the federal and state governments had aided the railroads so greatly gave them a strong justification for investigating and regulating the activities of the companies. Mechanical inventions and improvements had no small part in the development of the transportation system. The early tracks, constructed of wood beams on which were fastened iron strips, and sometimes described as barrel-hoops tacked to laths, were replaced by iron, and still later by heavy steel rails. By 1890 about eighty per cent. of the mileage was composed of steel. Heavy rails were accompanied by improved roadbeds, heavier equipment and greater speed. A simple improvement was the gradual adoption of a standard gauge--four feet eight and a half inches--which replaced the earlier lack of uniformity. The process was substantially completed by the middle eighties, when many thousands of miles in the South were standardized. On the Louisville and Nashville, for example, a force of 8,763 men made the change on 1,806 miles of track in a single day. The inauguration of "standard" time also took place during the eighties. Hitherto there had been a wide variety of time standards and different roads even in the same city despatched their trains on different systems. In 1883 the country was divided into five vertical zones each approximately fifteen degrees or, in sun-time, an hour wide. Both the roads and the public then conformed to the standard time of the zone in which they were. [Illustration: Map of the United States showing railroads in 1870]