From the torrent, or the fountain— From the red cliff of the mountain— From the sun that round me rolled In its autumn tint of gold—
Hmm—so things don't get any clearer now do they? The speaker delivers some more anaphoric lines to describe this whole mystery business that, quite frankly, is still a mystery to us.
The point of all these lines is that this mysterious "mystery" is found everywhere.
Rather than simply say "it was everywhere," though, or just list off 8 billion things, the speaker gets clever and refers to all several categories of things.
So far we've got all forms of water (a "torrent," which is just a waterfall or rush of water, and a fountain), all forms of earth and land ("red cliff of the mountain"), and all forms of light (the sun).
Next the speaker describes the sun as possessing an "autumn tint of gold."
Autumn is a time of transition, the time when summer is just about over but when winter hasn't quite arrived yet.
Leaves change colors, leaves fall, the weather changes, the days get shorter—you know the drill.
The point here is that the speaker is describing his own transition—from a lonely, confused kid to somebody with access to a very powerful mystery.
What's more, this transition is also happening on a poetic level.
For example, the poem's meter is changing a little bit, from mostly iambs to mostly trochees. You can read a bit more about this in "Form and Meter."
The tone is also changing, from one of frustration or depression to something a little different—a tone that still expresses alienation but also a sense of inspiration. Let's read on to see if that continues.