What did the settlement of the West mean to Frederick Jackson Turner?

To Frederick Jackson Turner, the settlement of the West
was a good thing and a bad thing.  The process of settling it was good, but the fact
that the West became settled was bad for the United
States.

To Turner, the existence of a frontier was basic to
the American character.  Turner believed that Americans' basic character was formed by
the fact that they had always been able to go out and "conquer" some new area of land. 
This allowed Americans to be independent and and allowed democracy to flourish.  It
allowed them to be ingenious and resourceful, which helped the US
economy.

This meant that the "closing" of the West was bad
news.  If there was no longer a frontier, how would Americans challenge themselves?  How
would they maintain their independent and resourceful spirits?  These were serious
problems in Turner's mind.