The beauty of Nature [is] beginning to fade, and chill winter will soon spread his heavy mantle. --Then farewell, you rural walks and shady groves.
This is unidentified.

But for "and chill winter will soon spread his heavy mantle,"

compare:

The season has shed its mantle
Of wind and chill and rain.
(Le temps a laisse son manteau
De vent, de froidure et de pluie.)
--Charles d'Orlean (1391-1465)
For "Then farewell, you rural walks and shady groves,"

compare Eve's speech on her being forced from the Garden of Eden in Paradise Lost:

Must I thus leave thee, Paradise? thus leave
Thee, native soil, these happy walks and shades,
Fit haunt of gods? where I had hope to spend,
Quiet though sad, the respite of that day
That must be mortal to us both. O flowers,
That never will in other climate grow,
My early visitation, and my last
At even, which I bred up with tender hand
From the first opening bud, and gave ye names,
Who now shall rear ye to the sun, or rank
Your tribes, and water from the ambrosial fount?
Thee lastly, nuptial bower, by me adorned
With what to sight or smell was sweet; from thee
How shall I part, and wither wander down
Into a lower world, to this obscure
And wild, how shall we breathe in other air
Less pure, accustomed to immortal fruits?"
--XI, vv. 269-285.