barely (figurative)
This report has barely skimmed the surface of the subject.

only
low
A bird skimmed low over the water.

across, over
We skimmed across the water in a small boat.

skim the surface (figurative)
Foreign films only skim the surface of Moroccan life.

Skim is used with these nouns as the object:
page, surface

Skim is used with these nouns:
milk