Axel is a reluctant hero. He is at his core incredibly cautious, and he knows that the Professor is (and will thus act) the opposite way. The protégé initially hopes to keep his uncle from even seeing the document and from realizing its significance:
If he should turn this document round and round, his may by chance discover the key! I shall destroy it.
Initially, he and Professor Lidenbrock are at a loss when they are attempting to decipher the cryptogrammatic Icelandic Runes, as presented by the map. They work to perceive patterns and word-groupings, without which it will be impossible to crack the code. But the solution to this problem evades them until Axel sees the parchment page from a different angle. Then the letters suddenly snap to attention and organize themselves linearly—the Latin words craterum and terrestre are formed.
What seemed originally to be incomprehensible nonsense can actually be seen and understood through a Latinate filter (though Verne seems more to infer that all the codebreaking elements "come together" in this moment when seen through this particular lingual filter—rather than literally describing how the words "physically" align).