His investigation of the slopes of the Jura led to an address before the Helvetic Association assembled at Neuchâtel in 1837, in which he said: "Siberian winter established itself for a time over a world previously covered with a rich vegetation and peopled with large mammalia, similar to those now inhabiting the warm regions of India and Africa. Death enveloped all nature in a shroud, and the cold, having reached its highest degree, gave to this mass of ice, at the maximum of tension, the greatest possible hardness." He showed how huge boulders had been distributed over the continent.
His views excited much opposition, from most of the older geologists. Even Humboldt said, "Your ice frightens me." But the discussion convinced the scientific world that Agassiz was both original and brilliant. He was soon called to a professorship of geology and mineralogy at Geneva, with a salary of three thousand francs, and also to Lausanne; but he refused both offers. So pleased were the people of Neuchâtel that they made him accept a present of six thousand francs, payable during three years.
In 1838, Agassiz founded a lithographic printing establishment in Neuchâtel, where his work could be done under his own direction instead of in Munich. He was now, besides his duties as professor, at work on "Living and Fossil Echinoderms and Mollusks," as well as "Fresh-Water and Fossil Fishes," and soon after upon the "Études sur les Glaciers," with an atlas of thirty-two plates. The book gave an account of all previous glacial study, and the observations of himself and companions.
"Agassiz displayed during these years," said one of his co-workers, "an incredible energy, of which the history of science offers, perhaps, no other example." He worked always till midnight, often till two or three o'clock, sitting for hours at his microscope, troubled much with congestion of the head and eyes. The expense involved in his work was enormous, and he was burdening himself with debts, which are more wearing and destructive to health and happiness than any amount of work can ever be.
Still he struggled on, through these dark days of poverty. He was only thirty-three, so young-looking that, on seeing him, people asked if he were "the son of the celebrated professor of Neuchâtel." He had already been chosen a member of the Royal Society of London.
In 1840 he made his first permanent station on the Alps, taking with him barometers, thermometers, hygrometers, psychometers, boring apparatus, and microscopes, making the Hospice of the Grimsel his base of supplies, and the lower Aar glacier the scene of his work. A huge boulder, its upper surface forming a roof, with a stone wall constructed on one side, became the sleeping-room of Agassiz and five friends. This abode was called the Hôtel des Neuchâtelois. Jacob Leuthold, an intrepid Swiss, was their chief guide. He died at thirty-seven, sincerely mourned by all. They made dangerous ascents of snow-covered peaks, measured the depth and forward movement of glaciers, Agassiz even being lowered by ropes one hundred and twenty-five feet into a glacial well, to investigate its formation.
All Europe was becoming interested in glaciers. Edward Forbes wrote from Edinburgh: "You have made all the geologists glacier-mad here, and they are turning Great Britain into an ice-house." Darwin was deeply interested. He wrote from North Wales: "The valley about here and the site of the inn at which I am now writing must once have been covered by at least eight hundred or one thousand feet in thickness of solid ice! Eleven years ago I spent a whole day in the valley where yesterday everything but the ice of the glaciers was palpably clear to me, and I then saw nothing but plain water and bare rock."
Agassiz now began work on his "Nomenclator Zoölogicus," and his "Bibliographia Zoölogiæ et Geologiæ," the former comprising "an enumeration of all the genera of the animal kingdom, with the etymology of their names, the names of those who had first proposed them, and the date of their publication." The latter contained a list of all the authors named in the Nomenclator, with notices of their works. This was published by the Royal Society in England, in 1848, the expense being too great for one person.
In 1843 the "Fossil Fishes," in five large volumes, was completed, and the following year his "Monograph on the Fossil Fishes of the Old Red Sandstone, or the Devonian System of Great Britain and Russia," was published, a large volume accompanied by forty-one plates. The discovery of these fossils was due to Hugh Miller, whose interesting life and pathetic death will always be associated with the study of the Old Red Sandstone.
In the spring of 1846, a great change took place in the life of the overworked naturalist. He had long hoped to visit the United States for scientific investigation, and now the time had come. The King of Prussia, at the request of Humboldt, granted him fifteen thousand francs for this purpose—he had previously given Agassiz one thousand dollars for his glacial researches.... Leaving his wife and daughters with Alexander Braun, her brother, at Carlsruhe, and his son Alexander at school at Neuchâtel, Agassiz said good-by to his students, who came at two o'clock at night, in procession with torchlights. Going to Paris, he spent some time in bringing out his second work upon the glaciers, "Système Glaciaire," receiving the Monthyon Prize of Physiology from the Academy, and sailed for America in September, 1846.