As a glacier flows, it drags rocks, boulders, pebbles, sand and silt across bedrock cutting away at it like a great rasp or file.
(a glacier; flows; ) (it; drags; rocks, boulders, pebbles, sand and silt across bedrock cutting away at it like a great rasp or file; T:As a glacier flows) (bedrock; cutting away; at it)
a glacier it bedrock
flows drags cutting away
rocks, boulders, pebbles, sand and silt across bedrock cutting away at it like a great rasp or file T:As a glacier flows
at it