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Updated: July 17, 2025
These, however, were sufficient to show me that the gneiss of Depilto was overlain conformably by the contorted schists; that the latter were followed by soft trappean beds, and these by thick beds of quartz-conglomerate, apparently derived from the degradation of the schistose rocks, with their numerous quartz veins.
Raphael Pumpelly, assisted by a corps of geologists, and the field of his work is the crystalline schists of the Appalachian region, or eastern portion of the United States, extending from northern New England to Georgia. He will also include in his studies certain paleozoic formations which are immediately connected with the crystalline schists and involved in their orographic structure.
"I can see clearly now," I cried; "the sediment from the waters which once covered the whole earth formed during the second period of its existence these schists and these calcareous rocks. We are turning our backs on the granite rocks, and are like people from Hamburg who would go to Lubeck by way of Hanover." I might just as well have kept my observations to myself.
But the researches of MM. Savi, Boue, Pareto, Guidoni, De la Beche, Hoffman, and Pilla demonstrated that this marble, once supposed to be formed before the existence of organic beings, is, in fact, an altered limestone of the Oolitic period, and the underlying crystalline schists are secondary sandstones and shales, modified by Plutonic action.
Nor does the almost universally volcanic composition of such islands favour the admission that they are the wrecks of sunken continents; if they had originally existed as continental mountain ranges, some at least of the islands would have been formed, like other mountain summits, of granite, metamorphic schists, old fossiliferous and other rocks, instead of consisting of mere piles of volcanic matter.
It is much more rational to suppose that the increased hardness imparted to the slates and schists at or near their contact with the lode is due to an infiltration of silica from the silicated solution which at one time filled the fissure.
This series, about 20,000 feet in thickness, is, as before stated, unconformable to that last mentioned; it consists in great part of gneiss of a reddish tint with orthoclase feldspar. Beds of nearly pure quartz, from 400 to 600 feet thick, occur in some places. Hornblendic and micaceous schists are often interstratified, and beds of limestone, usually crystalline. Beds of plumbago also occur.
The upper is more than five thousand feet thick and consists of shales and sandstones with some limestones. The lowest member is a basal conglomerate composed of pebbles derived from the erosion of the dark crumpled schists beneath, schists which are supposed to be Archean.
Tierra del Fuego, clay-slate formation, cretaceous fossils of; cleavage and foliation; form of land. Chonos Archipelago, mica-schists, foliation disturbed by granitic axis; dikes. Chiloe. Concepcion, dikes, successive formation of. Central and Northern Chile. Concluding remarks on cleavage and foliation. Their close analogy and similar origin. Stratification of metamorphic schists.
These schists contain trilobites belonging to the genera Paradoxides, Olenus, Agnostus, and others, some of which present rudimentary forms, like the genus last mentioned, without eyes, and with the body segments scarcely developed, and others, again, have the number of segments excessively multiplied, as in Paradoxides.
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