Meanings of dark boulders in English

He saw scattered green ferns, and a few dark boulders.

He motioned toward a slight rise between dark boulders and above one of the scattered termite hills.

The mixture of pristine white snow, dirty brown snow, small dark boulders, and gray ice chunks flowed like liquid concrete.

Above them, holes in the temple roof let in narrow shafts of sunlight, which fell on clusters of iridescent lichens clinging to dark boulders.

The storm above swallowed the tops of buildings and snapped with electricity, agitating the dark boulders of the clouds to knock hollowly into one another.