Crossword Puzzle Formation head?

Clue: Formation head?

Flock formation (VEE with 3 letters)
Citizenship and Immigration Services head office? (HOUSEOFGREENCARDS with 17 letters)
Stuffed head on a wall, perhaps (ELK with 3 letters)
Trite header (CON with 3 letters)
Liner in 1912 headlines (TITANIC with 7 letters)
Head, ear or heart follower (ACHE with 4 letters)
Some flight formations (VEES with 4 letters)
Third-col. heading (TUE with 3 letters)
Serpent with many heads (HYDRA with 5 letters)
The process of mountain formation (OROGENY with 7 letters)