Ah, it's also dead—good times. Well, since the "chasm-side is/ dead" we can safely guess that all of the damage killed that part of it. So although the "defiant" edifice-cliff looked as if it was holding steady, part of it just couldn't survive the abuse.
Now, since we have some suspicions that the cliff is part of the extended metaphor about humanity withstanding abuse, we know that these lines aren't just about a cliff and its chasm. Instead we understand that, just like the cliff, humanity might also lose a part of itself (iron edge or no) after so much abuse.
Again, this is all figurative language, since we know parts of people don't literally die, just like cliffs can't die either. But the language heightens our sense of looking at life and death from many different angles, not just in the literal sense of living things dying.
Also, we have another rare period at the end of line 36 that tells us to stop and consider what we just read. This is the first time we've actually seen the word "dead" used, so it's fitting that we take a moment to think about the severity of the word and how it's being used.
So what do we think? We're nearing the end of the poem, so perhaps the speaker is beginning to wrap things up in a way that's a bit more direct than we've seen so far. Death is, well, pretty direct, and since it relates to the idea of abuse, we know that there are some heavy ideas to consider.
One thing we might consider is the idea that, out of the two kinds of abuse we've seen, one can be controlled (the abuse perpetrated by people). The ocean can't control how it damages the cliff, but people don't need to take hatchet strokes to it and blow it up with dynamite, right?
So we're dealing with the same sort of idea when we imagine people in the contexts of "natural" abuse (like aging, disease, etc.) and "manmade" abuse (like violence, war, etc.). The latter can be controlled but not the former.
Repeated evidence has proved that it can live on what can not revive its youth. […]
Hmm, so what can live on something that can't "revive/ its youth"? Good question. Let's start with clarifying the subject. The "it" in line 38 is presumably the edifice-cliff, but since the "chasm-side" is dead, we can assume we're looking at another part that's still alive.
So we know for sure now that this is no ordinary cliff and is definitely a symbol for something human. Words like "live on," and "revive its youth," convince us that we're dealing with issues of life and death through a human perspective, since animals aren't usually concerned about reviving their youth.
But what does it mean? Again, we have more ambiguity here, so we can entertain lots of different ideas.
Maybe the still-living side of the cliff that's resting on the ocean realizes that the ocean can't fix it or "revive its youth." And still it "live[s] on" this very substance that can't do anything for it.
And since the cliff is a symbol for humanity, we can imagine how people live in a similar way. As we age, we realize the things we consume can't turn back time and make us healthy and young again. But we endure and keep living on.
Alternatively, in a more spiritual sense, the things we "live on," whether it's a faith of some sort or belief in something, can't revive our youth either. And yet we continue to live with these beliefs and keep on trekking through.
A third way to see these lines is to pinpoint exactly what the speaker's on about with "what can not revive its youth." What might that thing be? One idea is experience. Experience is something that you only gain by getting older. By definition, it cannot revive your youth. So the scars and abuse that the cliff-edifice-symbol-of-humanity are markers of experience, knowledge and wisdom that allow it to continue on in the face of hardship.
[…]The sea grows old in it.
Moore's very last line is equally compelling as the previous ones and can bring to mind lots of different ideas.
Here's one: If the cliff lives on the sea that can't revive its youth, it makes sense that both things would continue to grow "old" no matter what. In fact, the entire planet grows old too (approximately a few million years and counting).
So "old" here doesn't necessarily relate to wrinkles and brittle bones. Rather the word appears to be pointing more towards the idea of endurance. The "defiant" cliff continues to live on despite a part of it being "dead."
So if the cliff is a symbol for humanity, we get the sense that man and nature are being portrayed here as one big family. And no matter how much abuse occurs, humanity continues to survive and endure, just like nature.
When we put everything together, including the poem's form, rhythm, and dissolving imagery, we see even more this idea of everything working together in some sort of order. Sometimes things are serene, sometimes they're violent, but no matter what humanity and nature continue to endure it all.
And though we may expect things that are orderly to also be meaningful, Moore convinces us by the end of "The Fish" that the two may not be the same. Sometimes recognizing the order and moving with it (like those fish wading through black jade) is enough.