Technology, Books and Other Neat Stuff

My most remembered poem I learned at infant school, but I cannot remember who it was written by:

This I remember
I saw from a train -
A shaggy white pony
That stood in the rain.
Where I was going
And where was the train,
I cannot remember,
I cannot explain.
All these years after
It comes back again -
A shaggy white pony
That stood in the rain.

I have googled repeatedly for various lines from the poem, but cannot track down it's origins...