Describe the horses in Journey to the Center of the Earth.

The horses in Journey to the Center of the Earth are described as “small but vigorous.” They are Icelandic horses and built for the difficult and rugged terrain that Otto Lidenbrock, along with his nephew, Axel Lidenbrock, choose to cross on their journey to find the center of the earth. They start this journey with their guide, Hans Bjelke, and two more pack horses. The pack horses follow along behind them without any lead, indicating that the little Icelandic horses are of above-average intelligence and extremely well-trained.
Otto Lidenbrock is so impressed with his little mount, Henry, that he began to sing his praises, talking about how sure-footed, intelligent, and stout-hearted these Icelandic horses are, indicating that Otto and Axel are both well-acquainted with horses and with riding. Otto even goes so far as to say:

I dare to say that if any river, any fjord has to be crossed—and I have no doubt there will be many—you will see him enter the water without hesitation like an amphibious animal, and reach the opposite side in safety.

Ironically, it is only a short while later in the book that they come upon a fjord, an extended arm of the sea that is filled with rolling waves and surrounded by tall cliffs. Axel is sure that the intelligent animals will refuse to cross the fjord, and rightly so, but the smitten Otto sets about to prove the sure-footed courage of Henry, encouraging him to cross. The result is that Otto is tossed into the fjord, for Henry proves to be more stubborn even than the stubborn Otto!
At the same time, it does prove the theory on how intelligent Icelandic horses are, for horses do not tread where it is not safe to go. Luckily, they are able to ride a ferry across the fjord, along with all four “intelligent” Icelandic horses!