During the same period similar surveys were being made in northern Michigan by Dr. Charles T. Jackson, 1847–48, and Foster and Whitney, 1849–51. These surveys also had been hastened by the “copper fever” of 1844–46, with wholesale issue of permits and leases, Congress in 1847 authorizing the sale of the mineral lands and a geological survey of the Lake Superior district. The execution of these surveys under Jackson and under Foster and Whitney and the prompt publication in 1851 of the maps of the whole region materially helped to establish copper mining on a more conservative basis. and the development of the Lake Superior region was rapid.[99] These land-classification surveys, with their definite purpose, represent the best geologic work of the time. The plan necessitated thoroughgoing field work with considerable detail and prompt publication of systematic reports, and in the working up of the results specialists like James Hall and Joseph Leidy contributed, while F. B. Meek was an assistant of Owen. It is worthy of note that had not Doctor Houghton, the State geologist of Michigan, met an untimely death in 1847, effective cooperation of the State Survey with the Federal officials would have combined geologic investigation with the execution of the linear surveys.[100] Belonging to the same period of geologic exploration was the service of J. D. Dana, as United States Geologist on the Wilkes Exploring Expedition, the disaster to which compelled his return from the Pacific Coast overland and resulted in his geologic observations on Oregon and northern California. The military expeditions during the decade 1850–60 and the earlier expeditions of Fremont added to the geographic knowledge of the Western country and also contributed to geologic science, largely through collections of rocks and fossils, usually reported on by the specialists of the day. Thus the names of Hall, Conrad, Hitchcock, and Meek appear in the published reports on these explorations, while Marcou, Blake, Newberry, Gibbs, Evans, Hayden, Parry, Shumard, Schiel, Antisell, and Engelmann were geologists attached to the field expeditions. In 1852 geologic investigation was seemingly so popular as to necessitate the statutory prohibition “there shall be no further geological survey by the Government unless hereafter authorized by law.”