Charles Ellicott Commentary Psalms 104:8

"(The mountains rose, the valleys sank down) Unto the place which thou hadst founded for them." — Psalms 104:8 (ASV)

They go up. —This translation is grammatically possible, but is inconsistent with the preceding description. It is better therefore to take the clause parenthetically, and to make hills and valleys the subjects. Hills rise, valleys sink, an interesting anticipation of the disclosures of geology, which, though in a different sense, tells of the upheaval of mountains and depression of valleys. Two passages in Ovid have been cited in illustration (Met. i. 43, 344). And Milton, no doubt with the psalm as well as Ovid in his mind, wrote

“Immediately the mountains huge appear
Emergent,” etc. —Paradise Lost, book vii.