They were climbing a mountain top on the Savoy side of the lake: 

This solitary spot formed a wild and desert nook, but full of those sorts of beauties which are only agreeable to susceptible minds, and appear horrible to others.  A torrent, occasioned by the melting of the snow, rolled in a muddy stream within twenty paces of us, and carried dust, sand, and stones along with it, not without considerable noise.  Behind us, a chain of inaccessible rocks divided the place where we stood from that part of the Alps which they call the Ice house....  Forests of gloomy fir trees afforded us a melancholy shade on the right, while on the left was a large wood of oak, beyond which the torrent issued; and beneath, that vast body of water which the lake forms in the bay of the Alps, parted us from the rich coast of the Pays de Vaud, crowning the whole landscape with the top of the majestic Jura.

Rousseau’s influence upon feeling in general, and feeling for Nature in particular, was an extraordinary one, widening and deepening at once.

By his strong personal impulse he impelled it into more natural paths, and at the same time he discovered the power of the mountains.

He brought to flower the germ which had lain dormant in Hellenism and the Renaissance; and although his readers imbibed a sickly strain of morbid sentimentality with this passion for the new region of feeling, the total effect of his individuality and his idealism was to intensify their love for Nature.  His feelings woke the liveliest echo, and it was not France alone who profited by the lessons he taught.

He was no mountaineer himself, but he pointed out the way, and others soon followed it.  Saussure began his climbing in 1760, exploring the Alps with the indomitable spirit of the discoverer and the scientist’s craving for truth.  He ascended Mont Blanc in 1787, and only too soon the valleys of Chamounix filled with tourists and speculators.  One of the first results of Rousseau’s imposing descriptions of scenery was to rouse the most ardent of French romance writers, Bernardin de St Pierre; and his writings, especially his beautiful pictures of the Ile de France, followed hard in the wake of La Nouvelle Heloise.

In Paul and Virginia vivid descriptions of Nature were interwoven with an idyllic Robinson Crusoe romance: 

Within this enclosure reigns the most profound silence.  The waters, the air, all the elements are at peace.  Scarcely does the echo repeat the whispers of the palm trees spreading their broad leaves, the long points of which are gently agitated by the winds.  A soft light illumines the bottom of this deep valley, on which the sun shines only at noon.  But even at break of day the rays of light are thrown on the surrounding rocks, and their sharp peaks, rising above the shadows of the mountain, appear like tints of gold and purple gleaming upon the azure sky.