Job 39:10

Canst thou bind the unicorn with his band in the furrow?.... Put the yoke and harness upon him, and fasten it to the plough to draw it, that he may make furrows with it in the field, or plough up the ground as the tame ox does? thou canst not;

or will he harrow the valleys after thee? draw the harrow which is used after ploughing to break the clods, and make the land smooth and even? he will not: valleys are particularly mentioned, because arable land is usually in them; see Psalms 65:13.