Comparisons Of Size

All the snow had disappeared by now and ice on the lake was featureless under grey skies. I wandered aimlessly inland through the wood looking for anything of interest. The only active wildlife was squirrels, busy chomping on nuts and scampering from tree to tree.

I cam across this row of stones lined up on a boulder, arranged by an unknown hand and thought them worthy of investigation.

When does a pebble become a stone, or a stone turn into a rock, or a rock form a boulder. Perhaps it depends on the viewer and where they stand and how big they are?