At the same time, the survey of the basin of the Dead Sea was completed and rectified. In 1838, two American Missionaries, Edward Robinson and Eli Smith, gave quite a new impulse to Biblical geography. They were the forerunners of that phalanx of naturalists, historians, archaeologists, and engineers, who, under the patronage or in conjunction with the English Exploration Society, were soon to explore the land of the patriarchs from end to end, making maps of it, and achieving discoveries which threw a new light on the history of the ancient peoples who, by turns, were possessors of this corner of the Mediterranean basin. But it was not only the Holy Land, so interesting on account of the many associations it has for every Christian, which was the scene of the researches of scholars and explorers; Asia Minor was also soon to yield up her treasures to the curiosity of the learned world. That country was visited by travellers in every direction. Parrot visited Armenia; Dubois de Monpereux traversed the Caucasus in 1839. In 1825 and 1826, Eichwald explored the shores of the Caspian Sea; and lastly, Alexander von Humboldt at the expense of the generous Nicholas, Emperor of Russia, supplemented his intrepid work as a discoverer in the New World by an exploration of Western Asia and the Ural Mountains. Accompanied by the mineralogist Gustave Rose, the naturalist Ehrenberg, well known for his travels in Upper Egypt and Nubia, and Baron von Helmersen, an officer of engineers, Humboldt travelled through Siberia, visited the gold and platinum mines of the Ural Mountains, and explored the Caspian steppes and the Altai chain to the frontiers of China. These learned men divided the work, Humboldt taking astronomical, magnetic, and physical observations, and examining the flora and fauna of the country, while Rose kept the journal of the expedition, which he published in German between 1837 and 1842. Although the explorers travelled very rapidly, at the rate of no less than 11,500 miles in nine months, the scientific results of their journey were considerable. In a first publication which appeared in Paris in 1838, Humboldt treated only the climatology and geology of Asia, but this fragmentary account was succeeded in 1843 by his great work called "Central Asia." "In this," says La Roquette, "he has laid down and systematized the principal scientific results of his expedition in Asia, and has recorded some ingenious speculation as to the shape of the continents and the configuration of the mountains of Tartary, giving special attention to the vast depression which stretches from the north of Europe to the centre of Asia beyond the Caspian Sea and the Ural River."