But it was as a geologist that his most valuable practical work was done. His "Report on the Geology of Connecticut," published in 1842, was the result of five years of arduous labor and is a sufficient monument for any man.
"While engaged in this survey," he wrote, "I can confidently say that I have been laborious and diligent. While traveling, it was my practice to rise early, in the longer days generally at dawn; in the shorter generally I got my breakfast and was on my way by daybreak, I continued, scarcely with any relaxation, as long as I had daylight and then was generally obliged to sit up till midnight, not unfrequently till one o'clock A. M. in order to complete my notes and arrange my specimens. This was continued, not only week after week, but month after month, almost without cessation."
Under the law Percival could not be paid till his report had been approved by the governor. It is characteristic of the whimsical geologist that he refused to submit to this approval by one whom he considered incompetent to pass upon his labors and it was only by the ruse of a friend who got possession of the report and presented it to the governor, who at once approved it, that Percival secured his pay.
This work brought Percival a high reputation as a geologist. He was engaged by the American Mining Company to investigate the lead deposits in Wisconsin and this in turn resulted in his employment by that state to make a geological survey similar to that of Connecticut. He had made his first report and was engaged upon his second when he became ill and in May, 1856, he died and was buried in Hazel Green, Wisconsin. "Eminent as a Poet," runs his epitaph, "rarely accomplished as a Linguist, learned and acute in Science, a Man without Guile."
During his employment in Wisconsin his friends had bought a lot and built a house for him in New Haven. It was a queer structure, built after the poet's own plans, with the entrance at the rear, blind windows at the front, and of only one story in height. He was looking forward to spending here his last years, close to his college, with his few intimate friends, surrounded by his books. During an interval in his Wisconsin employment he came to New Haven to inspect his future home and is said to have broken down completely as he was compelled to leave by the duty that called him westward.