Rightly quoted by Rev AC Smith as appropriate to Silbury on page 144 of his (fascinating) paper on Silbury in the The Wiltshire Archaeological and Natural History Magazine in 1862
http://books.google.co.uk/books?id=KDYGAAAAQAAJ&dq=The+Wiltshire+Archaeological+and+Natural+History+Magazine+By+Edward+Hungerford+Goddard&pg=PA1&ots=2QvYknPk0s&sig=9RzuoCa7-9VydT1MBo8BVWO5Q_k&prev=http://www.google.co.uk/search%3Fhl%3Den%26q%3DThe%2BWiltshire%2BArchaeological%2Band%2BNatural%2BHistory%2BMagazine%2BBy%2BEdward%2BHungerford%2BGoddard%26btnG%3DGoogle%2BSearch%26meta%3D&sa=X&oi=print&ct=result&cd=1#PPP7,M1

Unchanged it stands: it awes the lands
Beneath the clear dark sky ;
But at what time its head sublime
It heavenward reared, and why—
The gods that see all things that be
Can better tell than I