Chap. I.

GEOLOGY.

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Fullers' earth beds are deposites of calcareo-argillaceous beds, mixed with frequent coursesof soft rubble-stone, containing a considerable proportion of calcareous matter. Blue andyellow clays, called fullers’ earth, are found with them ; these clays are of a blue colour,changing near the surface to yellow ; they are often laminated, but generally resemble amass of argillaceous sediment, divided by lamina? of shelly limestone or lines of Septaria;pyrites and jet lie in many of them; from these clays the transition to either sandstone orlimestone is usually very gentle.

Inferior Oolite possesses a brown tinge or colour from the oxide of iron it contains,which is also mixed with much siliceous matter ; it sometimes passes into a ferruginoussandstone, as in Northamptonshire and the adjoining counties. The arenaceous depositesof this system are not found to be micaceous or felspathic, as those of an earlier date: ayellow tint is the prevailing one, sometimes of a deep colour; the grain is usually fine, andquartz pebbles occur as well as portions of carbonate of lime.

Sandstone , which is the lowest portion of the oolitic system, is always stratified, thoughoften coarse-grained, and exhibiting an oblique lamination, the finer sorts splitting easilyinto flags or slates. Shells, and plates of oxide or carbonate of iron, are found in them,which appear the result of molecular arrangement round nuclei of other matters whichhave served as centres of attraction.

Lias Formation is usually found stratified in conformity with the rocks of the ooliticgroup ; it is of considerable thickness, varying from 500 to 1000 feet, and of an uniformlithological character. It is of marine origin, and consists of an alternation of thin beds oflimestone, with a light brown weathered surface, separated by dark-coloured, narrow,argillaceous partings, having a striped appearance ; its prevailing colour is blue, thoughsome beds, called White Lias, have a yellowish-white tint. The organic remains areprincipally marine or littoral. Among the shells are the Grypha*a, Cephalopoda ,Ammonite, Belemnite, and Nautilus ; the fossil fish are the Lepidotus, &c. ; of the reptilesthere are several. species of Ichthyosaurus and Plesiosaurus, and among the plants ofZamias and Conifera?.

Upper Lias shales. — Marlstone , Lower Lias shale , Lias Limestone , and Lower Lias Marls,are its subdivisions.

Poikii.itic or New Red Sandstone formation is a great mass of arenaceous and argillaceousdeposit, immediately below the blue lias; gypseous and rock salt, with some organicremains, are contained in it. The rocks are generally granular, of a yellow colour, andsandy nature, but not micaceous; some of them are a coarse breccia, containing fragmentsof limestone; others arc conglomerates of various pebbles; many a coarse red grit, used forbuilding; the grains of this red sandstone consist mostly of clear quartz, the exteriorcoated with red oxide of iron.

Variegated Marls are red, blue, green, or white ; they are laminated, contain gypsumand rock salt; white and grey sandstones of a peculiar character are occasionally foundamong these marls.

Variegated Sandstone , so named from the white and mottled partitions contained in them ;the lower part is a quartzose conglomerate.

The red sandstones and red marls, which form so considerable a thickness in England,are perhaps the result of the disintegration of various crystalline or metamorphic schists,and often of porphyritic trap rock, containing much oxide of iron; the red colouringmatter with which this alluvium is tinted may have been furnished by the decomposition ofhornblende or mica, which contains oxide of iron in large quantities. Fossil remains arerarely found in any stratified rocks where this oxide of iron abounds.

Magnesian Limestones vary in their character, and are sometimes loaded with magnesia,having either a white, yellow, grey, or smoky colour, occasionally red. The texture iscompact, and sometimes oolitic, the cells being lined with crystallised carbonate of lime.Some of these limestones have a fine sandy grain, others are quite powdery, containingcrystallised balls. Plates and strings of spar are very common in them, and it is this pecu-liarity which causes magnesian limestone, when used in building, to decay, the stoneperishing between the ribs of spar, and crumbling away. The fine-grained limestone ofKnottingley are thin-bedded, or flag-like, and it is often difficult to trace the beds in thepowdery magnesian rocks ; they are frequently traversed by vertical divisions from top tobottom, which are in some places filled with pebbles or clay.

Marl slates are laminated impure calcareous rocks, of a soft argillaceous or sandynature.

Lower Red Sandsto7ie , with red and purple marls and micaceous beds; the grits arewhite or yellow, and either of a pebbly or sandy nature. The repetition of clay, sand-stone, and oolitic limestone, shows the new conditions imposed upon the land and sea, andthe loose grits that the deposits were made at no great distance from land.

The red sandstone appears to have accumulated in a situation unfavourable to either thereception of vegetable or animal exuvia?.

The magnesian limestone and red sandstone are variously tinted with oxide of iron, the

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