Why does the author include the information about limestone in paragraph 4?

Visitors to Austin often notice that the Texas Capitol looks a lot like the United States Capitol in Washington, D.C., with its tall dome and long wings. Fewer notice that the Texas building is actually a little taller. And very few know how Texas paid for it: not with money, but with land.

In 1881, a fire destroyed the old capitol building. Texas needed a new one, but the state had little money to spend. What it did have was land. Even before the fire, lawmakers had set aside about three million acres in the Texas Panhandle to pay for a new capitol, and the state offered that land to whoever would build it.

A group of investors from Chicago agreed to the deal. In exchange for building the capitol, they received the land. They turned it into a cattle operation called the XIT Ranch, which covered a huge stretch of the western Panhandle and became one of the largest fenced ranches in the world.

The builders first planned to use limestone from Central Texas. But when the stone was tested, it was found to stain and change color when exposed to the weather. The owners of Granite Mountain, near Marble Falls, offered to donate red granite instead. Granite is harder to cut than limestone, which made the work slower, but it would last far longer. That pinkish-red stone became the building's best-known feature.

The new capitol was finished in 1888. Today it still holds the office of the governor and the chambers where the Texas Legislature meets. Every time lawmakers gather under that dome, they are working inside a building that the state bought with three million acres of open land.