Riddle 58

I saw with one foot,
violence suffering,
a creature in the plain :
far it goes not,
nor rides much,
nor can it fly
through the bright day,
nor does a ship bear it,
a boat, a nail'd vessel ;
yet is it useful
to its master,
many times.
It has a heavy tail,
a little head,
a long tongue,
not any tooth :
a part of iron
the earth-grave paces :
liquid it swallows not,
nor eats it aught.
food it craves not,
yet bears it oft
the water-stream in air ;
in life it boasts not,
in its lord's gifts,
yet it obeys
its chief:
in its name are three
regular runic letters,
of which RÁD is the fourth.