scheme-source-modes

scheme-source-modes is a variable defined in `cmuscheme.el'.
Its value is

(scheme-mode)

Documentation:
Used to determine if a buffer contains Scheme source code.
If it's loaded into a buffer that is in one of these major modes, it's
considered a scheme source file by `scheme-load-file' and `scheme-compile-file'.
Used by these commands to determine defaults.

You can customize this variable.