The Question and Answer section for Journey to the Center of the Earth is a great resource to ask questions, find answers, and discuss the novel.
Looks like you answered your own question.
He believes the most intelligent animal is the Icelandic horse.
"Good beast, good beast," he would cry. "I assure you, that I begin to think no animal is more intelligent than an Icelandic horse.
The soup is made from Icelandic moss.... Lichen soup.
Our host filled our plates with a portion of lichen soup of Iceland moss, of by no means disagreeable flavor, an enormous lump of fish floating in sour butter.