Union Pacific offers $20 billion cash and one share of its stock to buy Norfolk Southern Tuesday in a merger that could trigger the final wave of railroad mergers across the country

Union Pacific Corp. agreed to acquire Norfolk Southern Corp. in a cash-and-stock transaction valued at $85 billion, forming a transcontinental rail behemoth in what stands to be the industry’s largest deal ever.

Union Pacific said on Tuesday it would buy smaller rival Norfolk Southern in an $85 billion deal, to create the nation's first coast-to-coast freight rail operator and reshape the movement of goods from grains to autos across the country.