1st Book of Enoch Chapt. 21- 22

Enoch sees the underworld and the eternal place of the fallen angel. This place is Hell within Hell called, Tartarus. Gods will is that none shall perish, in this chapter we see Abel giving suite that Cains seed be annihilated from the seed of men. So this verse supports the idea that Cain's bloodline is other than the seed of men, the serpent seed.

7. And he answered me saying: 'This is the spirit which went forth from Abel, whom his brother Cain slew, and he makes his suit against him till his seed is destroyed from the face of the earth, and his seed is annihilated from amongst the seed of men.