This line is included in Bilbo's first real look at the mountain, as he and the dwarves traveled down the river in their barrels.

The day grew lighter and warmer as they floated along. After a while the river rounded a steep shoulder of land that came down upon their left. Under its rocky feet like an inland cliff the deepest stream had flowed lapping and bubbling. Suddenly the cliff fell away. The shores sank. The trees ended. Then Bilbo saw a sight: The lands opened wide about him, filled with the waters of the river which broke up and wandered in a hundred winding courses, or halted in marshes and pools dotted with isles on every side: but still a strong water flowed on steadily through the midst. And far away, its dark head in a torn cloud, there loomed the Mountain! Its nearest neighbours to the North-East and the tumbled land that joined it to them could not be seen. All alone it rose and looked across the marshes to the forest. The Lonely Mountain! Bilbo had come far and through many adventures to see it, and now he did not like the look of it in the least.