Full details as to the Laurentian rocks of Canada and sectional lists of their beds will be found in the _Reports of the Geological Survey_, and Dr. Hunt has discussed very fully their chemical characters and metamorphism in his _Chemical and Geological Essays_. The recent reports of Hitchcock on New Hampshire, and Hayden on the Western Territories, contain some new facts of interest. The former recognises in the White Mountain region a series of gneisses and other altered rocks of Lower Laurentian age, and, resting unconformably on these, others corresponding to the Upper Laurentian; while above the latter are other pre-silurian formations corresponding to the Huronian and probably to the Montalban series of Hunt. These facts confirm Logan's results in Canada; and Hitchcock finds many reasons to believe in the existence of life at the time of the deposition of these old rocks. Hayden's report describes granitic and gneissose rocks, probably of Laurentian age, as appearing over great areas in Colorado, Arizona, Utah, and Nevada--showing the existence of this old metamorphic floor over vast regions of Western America. The metamorphism of these rocks does not imply any change of their constituent elements, or interference with their bedded arrangement. It consists in the alteration of the sediments by merely molecular changes re-arranging their particles so as to render them crystalline, or by chemical reactions producing new combinations of their elements. Experiment shows that the action of heat, pressure, and waters containing alkaline carbonates and silicates, would produce such changes. The amount and character of change would depend on the composition of the sediment, the heat applied, the substances in solution in the water, and the lapse of time. (See _Hunt's Essays_, p. 24.) [Illustration: Plate III. From a Photo by Weston. Vincent Brooks, Day & Son, Lith. WEATHERED SPECIMEN OF EOZOON CANADENSE. (ONE-HALF NATURAL SIZE.) _To face Chap. 3_] CHAPTER III. THE HISTORY OF A DISCOVERY.