In 1868 he was appointed State Geologist for New Hampshire, and spent ten years in the survey of that State. The results of his work there were published in three large quarto volumes, with a folio atlas of maps, profiles, and sections. The rocks described consist principally of crystalline schists and marine igneous ejections. The geology of New Hampshire is of peculiar importance, because the situation of the State is such that a correct knowledge of its rocks promotes the understanding of many obscure terranes in the adjacent regions of Maine, Quebec, Vermont, and Massachusetts. Professor Hitchcock's report of the survey may justly be styled his chief work. The part best studied relates to the White Mountains and the Ammonoosuc mining district. Connected with the survey was the maintenance of a meteorological station throughout the year on the summit of Mount Washington. Daily statements of the weather conditions of this station during the winter of 1870-'71 were sent by telegraph to the principal newspapers, and called out much interest--before the United States Signal Service began its weather predictions. The catalogue of Professor Hitchcock's publications comprises more than one hundred and fifty titles of papers, reports, and books. Perhaps the earliest thorough study represented among them was that of the fossil footmarks. The first of the published papers on this subject related to the tracks of animals in alluvial clay, and was published in the American Journal of Science in 1855. For several years after this he assisted his father in arranging the museum and compiling tables for the Ichnology. He made a complete catalogue descriptive of the more than twenty thousand individual impressions preserved in the Appleton Cabinet, which was printed, with descriptions of a few new species of footmarks, in the Supplement to the Ichnology of Massachusetts, edited by him after the death of his father in 1865. Although circumstances have prevented him from paying much attention to ichnology in later years, he has prepared several papers on the subject, the most important of which was one on the Recent Progress of Ichnology, which was read before the Boston Society of Natural History about twelve years ago. In it the ichnites were carefully catalogued anew and classified in the light of our knowledge of the numerous dinosaurs of the West; and the results of some studies of the slabs exhumed at Wethersfield, Connecticut, are well known. The list of the Connecticut footmarks was increased from one hundred and nineteen in the Ichnology to one hundred and seventy; and facts were cited to show that the _Grallator_, the three-toed animal most allied to birds, possessed a caudal appendage of a reptilian nature. The Trias of New Jersey had been found to illustrate new features in the _Otozoum_, whose tracks are often ornithic in aspect. A comparison of the features of the Triassic skeletons described by Marsh from Connecticut (_Anchisaurus_) shows