He received his first lesson in geology while he was still a sailor boy, at Lyme Regis--a spot exceedingly rich in fossils. A laborer whom he was observing broke a stone, the opening of which disclosed a fine ammonite. To his question as to what the fossil was, the laborer replied that if he had read his Bible he would have known; that there was once a flood that covered all the world; the things that were drowned were buried in the mud, and this was a snake which had suffered that fate. "A snake! but where's his head?" He was again referred to the Bible, which would tell him why the snakes in the rocks had no heads. "We're told there that the seed of the woman shall bruise the serpent's head. That's how 'tis." The second lesson came a few years later, in a reading club of which Pengelly was a member. They were reading Dick's Christian Philosopher, and came to a geological section, when the reader remarked that "as geology was very likely to be extremely dry, and as many good people thought it dangerous if not decidedly infidel in its teachings, he would propose that the selection should not be read. This was passed by acclamation, and the reader passed on to astronomy."
While still young, Pengelly removed to Torquay, where he spent the remainder of his life. Shortly after arriving there, he opened a small day school on the Pestalozzian system, into which he introduced the novelty of the use of chalk and the blackboard in giving instruction. Beginning with six pupils, the school grew rapidly. He had private pupils, too, and in 1846 these had become so numerous that he gave up his school, and as a special tutor in mathematics and the natural sciences found his life occupation. Some of his pupils became distinguished in after life; while others, like the two Russian princes, nephews of the Czar Alexander II, and Princess Mary, of the Netherlands, all of whom became much attached to him, were famous by reason of their position. His attention was brought for a third time to geology while looking over some books which he thought might be useful to his pupils, when he found one published by the brothers Chambers, which contained a chapter on that science. This was not much, but it was enough to inform him how much had already been done in geology, and, perhaps, to give him a hint of some of the possibilities that lay in it. From this time on, he was ardently interested in geology. The journal of his first visit to London and the British Museum, in 1843, attests how he was becoming absorbed in it. He spent his holidays in geological explorations and in excursions which gradually grew larger, until his position as a geologist was recognized, and he became an authority respecting all points and phenomena which had come under his personal knowledge. A hint dropped to him by Professor Jameson as he was about to visit the Isle of Arran taught him to make his notes of observations on the spot, and greatly helped, his daughter Hester observes in the biography on which we have drawn very largely, "to form those habits of extreme accuracy which characterized all his scientific work."