What's going on here? Terminal screen pops up after installing Mountain lion.

I installed mountain lion yesterday! all looked like it was working well. Just now I rebooted my iMac. The first thing I see on my computer is that it booted up in terminal mode! I have white lettering on black background with a lot of lines of text. At the end of many lines of text there is a copyright Regentss of the university of California."? Than it goes on with " MAC Franework successfully initialized."

The text goes on until " Root device is mounted read-only." than it ask if i want to boot system enter exit & hit return.

Anybody know what's going on here. I have never experienced this in my many years as a Apple enthusiasts!

I need some clarification