The gorge of Niagara River, below the falls, is perhaps the grandest known example of a valley eroded by water in compact rock;
(The gorge of Niagara River; is perhaps; the grandest known example of a valley) (a valley; eroded; by water in compact rock)
The gorge of Niagara River a valley
is perhaps eroded
the grandest known example of a valley
by water in compact rock