Reply to Objection 2: Even before the earth was accursed, thorns and thistles had been produced, either virtually or actually. But they were not produced in punishment of man; as though the earth, which he tilled to gain his food, produced unfruitful and noxious plants. Hence it is said: "Shall it bring forth TO THEE."
Reply to Objection 3: Moses put before the people such things only as were manifest to their senses, as we have said (Q[67], A[4]; Q[68], A[3]). But minerals are generated in hidden ways within the bowels of the earth. Moreover they seem hardly specifically distinct from earth, and would seem to be species thereof. For this reason, therefore, he makes no mention of them.