The first of the more important geological researches with which Pengelly's name is intimately associated was the exploration of the peculiar formation at Bovey Tracey, for the identification of its fossils and the determination of its age. The plain in which the formation lay had an aspect suggesting the basin of an ancient lake, and its deposits, "very different from the solid rocks of the surrounding hills," confirmed the suggestion. They consisted of gravels, sands, and clays, distinctly stratified, with seams of lignite, for which they had been worked. The pits had already attracted some notice, and the deposits had been mentioned in scientific literature, but very little had been learned concerning their age. In 1860 the subject was mentioned by the late Dr. Falconer, an eminent paleontologist, to Miss Burdett-Coutts as one the investigation of which would be a boon to science. Miss Coutts supplied the money that was needed, and the direction of the systematic investigation was intrusted to Pengelly; on learning which, Sir Charles Lyell wrote to him: "I am very glad of the prospect of our knowing something of the Bovey coal plants. It is almost a reproach to English geology that they have been so little explored, as they are perhaps the only fossils of the Tertiary period to which they belong." In order to determine accurately the nature, thickness, and order of the successive beds, and to make a satisfactory collection of fossils, a new section of the deposit was made, measuring one hundred and twenty-five feet, down to the bottom of a seam of lignite four feet in thickness, the "last bed" of the workmen, but not at the actual base of the deposit. Thirteen of the thirty-one beds of lignite which were cut through, and two of the beds of clay, yielded distinguishable plant remains. These were sent to Dr. Oswald Heer, of Switzerland, for examination; and he determined from the collection fifty species, including ferns, conifers, figs, cinnamon trees, an oak, a laurel, vines, andromedas, a bilberry, a gardenia, a water lily, and some leguminous plants. Heer referred the group to the Lower Miocene period, but some modification was afterward made in this determination in the light of a fuller knowledge of the Tertiary flora. The deposits and work at Bovey Tracey were the subject of a memoir to the Royal Society by Sir Charles Lyell; and Dr. Heer's account of his work--The Fossil Flora of Bovey Tracey--was published in 1863. While this investigation was going on, Lyell was preparing the fifth edition of his Manual of Geology. He invited Pengelly to suggest corrections to the text, saying that, besides positive mistakes, he would "be glad of any hints and suggestions made freely, which your knowledge of the manner in which beginners are struck may enable you to send us." The criticisms supplied by Mr. Pengelly were adopted by Lyell except where they had already been made unnecessary.