Added more info to the OP.
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Gameplay will be a lot like lorebuilding, except it's all IC. Your characters will be expected to experiment and create new spells, documenting them in a tome. The strength and quality of the spells you can create/cast increases as you approach the Chasm. Additionally, there is another sentient force in the world using magic to create and genetically modify life. This phenomenon should be investigated, and terminated if need be.

Some tribes are more technologically advanced than others; some have developed in different technological pathways. Feel free to come up with creative new tribes to encounter. The highest known tech level is Renaissance, with guns, germ theory, and rudimentary electricity. The lowest tech level is early-Medieval.