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Rh the coal-seams were formed, and devoted a large share of his scanty leisure to making a geological map of the district. His drawings were offered to Sir Henry de la Beche, when the latter began his government survey in that region, and Sir Henry gladly availed himself of them, giving due credit to Logan. While he remained in its vicinity, Loo-an did much for the museum of the Royal Institution of South Wales, and held the positions of Honorary Secretary and Curator of the Geological Department. He presented to it valuable collections of minerals and metallurgical products, laboratory apparatus, drawings, and a collection of Canadian birds. Logan rapidly became 'known among British geologists, and in 1837 was elected a Fellow of the Geological Society. The next year his uncle died, and Logan gave up his position in the Morriston copper-works.

The problem of the formation of coal-strata, which had engaged Logan's attention, was at this time far from settled, one party firmly maintaining that the carbonaceous matter had collected as drift-wood collects; another, that the seams were deposited like peat in the swamps. "In these circumstances," says his biographer, Professor Harrington, "Logan had the sagacity to observe and turn to account a fact which has settled forever the question of the origin of coal, in favor of the theory of growth in situ. Under eighty or more coal seams, which occur in the Welsh coal-field, the miners had observed the invariable presence of a bed of more or less tenacious and bleached clay, which they called the 'under-clay' of the coal, and which was often of practical importance as affording facilities for under-cutting the coal. The constancy of this fact Logan confirmed by his own observations, and added to it the further and important discovery that in all these under-clays there occurred abundance of remains of the peculiar plant known as Stigmaria, in such circumstances as to show that the plant was in situ, and not drifted. In February, 1840, Mr. Logan communicated his results to the Geological Society of London, in a paper entitled "On the Characters of the Beds of Clay immediately below the Coal-Seams of South Wales."

In his letters from Wales to his brother James, Logan had repeatedly asked for specimens of the Canada minerals, and had expressed the wish to examine for himself the rocks of his native region. Accordingly, in the summer of 1840, he left England for Canada. During his year's visit to America, he made geological studies in the neighborhood of Montreal, in Maine, and, just before his return, visited the coal-fields of Pennsylvania and of Nova Scotia. The results of two of his investigations he embodied in a paper entitled "On the Packing of Ice in the St. Lawrence, and on a Land-Slide in the Valley of the Maskinongé," which he read before the Geological Society of London in June, 1842. From the parts of this paper quoted by Thomas Keefer in his "Report on the Bridging of the St. Lawrence," George Stephenson is said to have obtained useful hints in