Who wrote this poem?

[istara]

There is a poem I remember pretty much verbatim from childhood, I must have learnt it by heart back then. Weird how that has stuck in my mind and not quadratic equations, but c'est la vie.

However I can't remember who wrote it. Here's what I remember:

As I lay quietly in the grass
Half dreaming, half awake
I saw four children barefoot pass
Across the tufted brake
The sky was glass, the pool was glass
And not a leaf did shake

The autumn berries clustered thick
Seldom I'd met with more
I thought these children came to pick
Many as picked before
Each had a long and crooked stick
And crowns of ash they wore

But not one berry did they take
Gliding, I watched them go
Hand in hand across the lake
With sallies to and fro
So half asleep and half awake
I guessed what now I know

They were not children, live and rough
Nor phantoms of the dead
But spirits, woven of airy stuff
By wandering fancies led
Creatures of silence, fair enough
No sooner seen than sped

Anyone recognise it?