It is actually not an Atari 2600 cartridge. It is a cartridge for Atari's home computers (Atari 400, 800, etc.). You won't be able to use it on the 2600. It says "Left Cartridge" because the Atari 800 model had two cartridge slots, although I can't remember anything that used both of them.
Oh, and welcome to AtariAge. Always nice to see new people here.
Edited by Animan, Sun Aug 29, 2010 10:51 AM.