See "there was nothing for it but to go on using it" above. For Charles Gould, it is impossible to "throw up the game," neither in the manner of Decoud nor of Don Juste Lopez. He must continue on his chosen course; in fact, he is "required" to by the "material interests!" We must not understand this phrase to mean that Gould acts out of obligation to the financial investors such as Holroyd and the railroad -- he is ready to blow up the mountain and leave them in the lurch. To Charles, the "material interests" are primarily the demands of material itself. He is the slave of the silver.