Grimrock

I placed 4 power gems in the shrine in the bog, but they didn't turn into the earth essence. They just form bubbles and turn different colors. What am I doing wrong? It worked in the fire shrine.

Oops, excuse my dumbness. I realized that I already had the earth essence.

...funny...

I had wondered if it were possible to create 2 of the same essences. Now I know.

An easy mistake to make, I think.