Chap. I.

GEOLOGY.

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Secondly , the upper Oolitic Scries, as Portland stone, Portland sand, and Kimmeridgeclay.

Thirdly , the middle Oolitic, as the Upper Calc grit, Coral Rag, Lower Calc giit,Oxford clay, and Kelloway rock.

Fourthly , the lower Oolitic, or Cornbrach, Forest marble, Great Oolite, and Bradfordclay, Stonesfield slate and Fuller’s earth, Inferior oolite, and Calcareous sand.

Fifthly, the Liassic group of Upper lias shale and Marlstone , Lower lias shale, andLower lias limestone.

The Older Secondary, or New Red Sandstone formation, or Triassic system, comprises theSaliferous marls, the Red sandstones, and Conglomerates.

The Newer Paleozoic period or Magnesian Limestone, or Permian System , comprisesthe Magnesian limestone and the Lower Red Sandstone.

The Carboniferous system, which comes also under this head, contains the Upper coalgrits, Coal measures, Millstone grit, Carboniferous limestone, and Lower carboniferousshales.

The Middle Paleozoic Period, Devonian system, or Old Red Sandstone formation, includesthe slate and limestones in Devonshire, as well as the Conglomerate, Cornstone, and Tillstone of Herefordshire and Scotland.

The Older Palaeozoic or Upper Silurian , are the Ludlow and Wenlock Series, and UpperCambrian rocks, and the Lower Silurian or Protozoic Series, comprises the Caradoc,sandstone, and Llardillo flags, as well as the Older Cambrian fossiliferous slates.

Stratification is found to be universal in the rocks of aqueous origin which compose theearth’s crust; and this character is the first to attract the attention of the geologist; it con-stitutes the bed of all stones, and has been formed entirely by mechanical means. It isnothing more than the deposit of the solid matter, brought down by the rivers, and spreadout over the bed of the sea. The mountains and high lands are continually crumblingaway, and their particles are for a time mechanically suspended in the running streams andrivers, and are thus borne away to form fresh land.

We find that the several strata, varying in thickness, are often disturbed from the hori-zontal position in •which they were deposited by some subterraneous movement, and thematerials that constitute them are usually sand, clay, limestone, and iron ; the successivelayers have the appearance of having been formed under water, as they are alternately sandand mud, which have been allowed to settle at regular intervals.

The dip of a stratum is its inclination with the horizon, and is always at right angleswith the strike ; the angle which the dip makes with the horizon is its amount of deviationfrom the level plane.

The strike is the direction in which a stratum lies, or the line of intersection of the planeof the bed with the horizon.

Faults are occasioned by the breaking away or settling of one portion of the earth’s crustfrom another, and this is sometimes found to occur to the extent of several hundred feet ormore.

Denudation occurs when a portion of a valley is washed away by a flood, and Elevation isa term given to the upheaving of a portion of the earth’s crust.

Cleavage: this is perhaps best illustrated by examining slate, which is not stratified in theordinary way, but is found to have three sorts of stratification, independent of each other,and occurring in different directions; one is the bedding, which it is often difficult to as-certain; the other is the cleavage plane; and the third is the divisional plane or joint.

Cleavage takes place easily on those argillaceous rocks where the planes are parallel toeach other; and these are often found to exist without being the result of stratification ;probably the cause of these masses being so divisible into planes is a partial crystallisation,for when clay moistened with acidulated water is subjected to voltaic action for some time, itwill show a laminated structure, the planes of the lamina being found at right angles to theelectric forces.

It is now necessary to give a description of each stratum, commencing with the

Tertiary Series , which were probably occasioned by the deposits from large rivers intoestuaries, as they consist of beds of gravel, clay', sand, and friable sandstone, and wereformed after the present land had become divided into bays and gulfs, or lagoons of variousextent and depth; arenaceous deposits prevail; argillaceous types are found in particulardistricts; calcareous rocks, having a marine as well as freshwater formation, He spread outin many basins, and marl as well as gypsum are found locally accumulated. Conglomeratecontaining fragments or entire boulders constitute some of the arenaceous rocks, and areof various colours, probably produced by the oxide of iron which they contain; some ofthese sands, which are rarely hard enough to constitute stone, are variously tinted, othersare colourless ; the green colour is produced by a silicate of iron.

The flints left by the destruction of the chalk, after being subjected to the action ofwater, occur in the state of rounded pebbles, accompanied with layers of lignite and sul-