Publisher's Synopsis
Excerpt from A Manual of Elementary Geology: Or the Ancient Changes of the Earth and Its Inhabitants
He was soon informed by Mr. Logan, at that time engaged in the geological survey of Canada, that the white sandstone above Montreal was really much older than the Old Red, or Devonian. It had in fact been ascertained many years before, by the State surveyors of New York (who called it the Potsdam to lie at the base of the whole Silurian series. As such it had been pointed out to me in 1841, in the valley of the Mohawk, by Mr. James Hall, * and its position was correctly described by Mr. Emmons, on the borders of Lake Champlain, where I examined it in 1842. It has there the character of a shallow water deposit, ripple-marked throughout a considerable thickness, and full of a species of Lingula. The ?at valves of this shell, of a dark color, are so numerous, and so arranged in horizontal layers, as to play the part of mica, causing the rock to divide into laminae, as in some micaceous sandstones.
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