Analysis of In a Museum

Here's the mould of a musical bird long passed from light,
Which over the earth before man came was winging;
There's a contralto voice I heard last night,
That lodges with me still in its sweet singing.

Such a dream is Time that the coo of this ancient bird
Has perished not, but is blent, or will be blending
Mid visionless wilds of space with the voice that I heard,
In the full-fuged song of the universe unending.