Well if you're rooted, you should have a Clockwork folder on your SD card, the other one is the internal memory then.
Another way to tell is the path to your pics. SD card pics are housed at /DCIM/100MEDIA whereas the internal pics are at /emmc/DCIM/100MEDIA. So the one with an /emmc directory is internal.
There are more ways to tell but that should get you there. For future reference, a handy trick when just starting out is to make a folder called AA_SDCARD (or similar). Since they're listed in alphabetical order, you'll always see it front and center and avoid mistakes...the worst of which is formatting the internal memory accidentally. You don't want that.