Obs.—Certain beds of dark-coloured schists containing a few corals, fuci, and shells, are referred to the uppermost part of this formation by some eminent geologists, but it is more consonant to the established system of classification to regard these fossiliferous beds as the lowermost of the Silurian rocks. The fineness of grain, general aspect, hardness, and texture of these strata, are well known, from the general employment of slate for economical purposes. These rocks extend over a great part of Cumberland, Westmoreland, and Lancashire, reaching to elevations of 3,000 feet, and giving rise to the grand scenery of the Lakes, and of North Wales.
| (Wond. p. 806.) |
Non-fossiliferous.
Metamorphic (transformed) or stratified crystalline rocks.
Subdivisions.—
| 1. | Mica-schist System. (Wond. p. 843.) Probably sedimentary rocks altered by high temperature. Mica-slate, Quartz-rock, Crystalline limestone, Hornblende schist, &c. |
| 2. | Gneiss System. Layers of Gneiss, Sienite and Quartz-rock, alternating with Clay-slate, Mica-schist, &c. |
Plutonic Rocks; unstratified crystalline masses.
Granitic System. (Wond. p. 844.) Granite—a rock composed of mica, quartz, and felspar; Porphyry; Serpentine; Trap. These rocks occur in amorphous or shapeless masses, and in dykes and veins.
>Obs.—No fossils have been detected in these rocks: but the intense igneous action which the masses appear to have undergone, may have obliterated all evidence of animal and vegetable structures, should any have been present, as well as the lines of stratification. By the aid of the microscope, we may yet perhaps solve the mystery which shrouds the origin of these rocks, and the student may take up the investigation with the certainty of obtaining much valuable information, even should the search for organic structures prove abortive. It is not, however, improbable that the siliceous frustules of diatomaceæ may have escaped destruction, and remain to reward the researches of some skillful and patient observer.