slate, near its junction with granite in the adjacent mountains, and is probably cotemporaneous with the veins. According to Dr. MacCulloch, the quartz rock in many parts of the Highlands present evident indications of being composed of fragments and rounded pieces again united, and is in fact a quartzose greywacke or grit. Part of the Lickey Hill near Bromsgrove is composed of granular quartz; and similar beds occur near the village of Hartshill, in Warwickshire, between Atherstone and Nuneaton. Quartz rock, as distinguished from quartzose gritstone, is an inconsiderable formation, and may with more propriety be referred to the Transition, than the Primary Class.

Jasper. This mineral is of rare occurrence as a constituent part of beds, or of mountain masses; it differs little from a siliceous flinty slate, but is generally coloured red, brown, or yellow, and is opaque. It contains a large portion of the oxide of iron in its composition. The beds of shale in the coal strata are sometimes converted by fire into a substance in every respect resembling jasper. There are beds of jasper of considerable magnitude in some parts of the Apennines covered by rocks of serpentine. In some situations beds of slaty jasper alternate with slate, to which rock they appear to bear the same relation as flinty slate. Lydian stone, which is a black siliceous flint slate, is by some geologists called black Jasper. The only bed of jasper that I have seen among the English rocks, occurs associated with beds of manganese ore at Doddiscombleigh in Devonshire. Jasper sometimes occurs in veins, and forms nodules in basaltic rocks.

Hornblende rock and Greenstone.-Hornblende rock has been described as associated with primary rocks, it also occurs in the lower transition rocks. Transition hornblende presents no variety of character by which it can be distinguished from Primary. Greenstone composed of felspar and hornblende, in which the felspar is white, and sienitic greenstone, in which the felspar is red, sometimes occur in beds among transition rocks, particularly of slate. But more frequently rocks of greenstone, sometimes called Trap, occur in an unconformable position, covering rocks both of the transition and secondary class, and will be described in the chapter on Unconformable Rocks; after the description of the lower secondary strata containing coal.

OBSERVATIONS ON CONFORMABLE TRANSITION ROCKS.

The order of succession in conformable transition rocks is extremely variable, and the thickness of the same beds differs greatly in different situations. In one district we find a whole uninterrupted series of calcareous strata, forming entire mountains; and in an adjacent district the same series are widely separated by intervening beds of slate, greywacke, or sandstone; and many of the strata which occur in one place, will often be wanting in another. We have before observed, that calcareous transition strata are subject to sudden variations of quality in the same mountain: we cannot therefore be surprised, that in distant districts a great diversity should exist, both in the number and thickness of calcareous strata of the same formation; no single stratum can be regarded as an universal formation. In whatever manner the strata were deposited, the deposition has been interrupted by causes to us unknown, which have accumulated thick masses in one situation, and prevented their formation in other parts. With respect to beds composed chiefly of the fragments of older rocks, it is evident that the contiguity to rocks which

were most easily disintegrated, would produce thicker beds of fragments in certain situations than in others, and that their formation must be local.

The organic remains found in transition rocks, belong almost exclusively to genera no longer existing, and which do not occur in the upper secondary strata. Vegetable remains are rare in transition rocks; they occur sometimes in slate rocks. The trilobite is peculiar to transition rocks; the gigantic species occurs in slate, and the smaller species in limestone. The orthoceratite is chiefly found in transition limestone; univalve shells rarely occur in it. The prevailing fossils in this class are madre. pores, corallites, and encrinites. The remains of vertebrated animals are rarely, if ever, found in transition rocks. Many instances cited by foreign geologists of vertebrated animals found in this class of rocks are erroneous; the rocks in which they occur belong to the secondary strata. And its hould be known, that some English conchologists have described fossil remains from specimens collected in particular counties, without knowing precisely their true localities, or whether they were found in situ or in diluvial deposits. In the near vicinity of the transition limestone in Derbyshire, I have collected gryphites and numulites, and even the fossils of the chalk formation, but they had no relation to the ancient limestone; they were found in beds of gravel.

Conformable transition rocks cover the primary, and sometimes alternate with them; they are also associated with the lowest beds of the coal formation, so that no well marked division can be traced between them: but there is one character, independent of all artificial arrangements, which serves to distinguish transition rocks from the upper secondary strata, in countries where the regular coal formation is found. All rocks under the coal formation belong either to the transition or primary class; and all the strata above the coal formation, belong either to the upper secondary or the tertiary class. The geological position of the regular coal formation thus serves as a simple and intelligible key to the geology of all countries where the coal formation occurs. But where the coal strata are absent, the difficulty of determining the class to which certain rock formations belong, is often very great. Of this we have a striking instance in the perplexed attempts of foreign geologists to classify the vast calcareous formations of the

Jura, and the outer range of the Alps; and the perplexity is further increased, by the mistakes which are made in referring to the English mountain limestone, by confounding it with the calcaire alpin or alpine limestone. The alpine limestone, according to some geologists, is a transition limestone; but according to other geologists, it is analogous to the magnesian limestone under the new red sandstone, and also comprises the lias limestones and the oolites. Indeed, I am convinced that in the vicinity of the Alps, rocks analogous to the chalk formation, have not unfrequently been classed with transition limestones. These mistakes have arisen from a desire to make observations agree with preconceived theories, and the artificial arrangements which Werner had invented. Thus it was taken for granted, that the granitic mountains of the Alps being primary, the calcareous mountains must be primary also; and when organic remains were first discovered in them, the geologists in France were greatly surprised, and seemed unwilling to admit the fact at length, by a painful and reluctant effort, they removed all these mountains from the primary to the transition class. A more Herculean labour remains to be performed, that of removing many of these mountains still higher, into the upper secondary class. In the vicinity of Moutiers in the Tarentaise, where M. Brochant first observed some organic remains supposed to belong to transition rocks, I discovered the Patella and other fossils, peculiar to the upper secondary strata.

In parts of France at a distance from the Alps and the Jura, the mineral character of the secondary strata might alone serve to identify them with the English lias, oolites, and chalk; but in the range of the Jura and the outer ranges of the Alps, the calcareous formations are of such immense magnitude, and the beds are often so highly indurated and crystalline, that it is only from their relative position and imbedded fossils that we can trace their analogy to the English strata, or to the secondary strata in the north of France.

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CHAPTER VIII.

ON THE LOWER SECONDARY STRATA COMPRISING THE REGULAR COAL FORMATION.

The relative Geological Position of Coal Strata.-Wood Coal.Mineral Coal.-Arrangement of the Strata in Coal-fields.Concavities or Basins in which Coal Strata are deposited.-Intersections by Faults or Dykes.-Their Effects on Water in Coal Mines.-Peculiar Positions of Coal Strata in certain Districts. On the Mode of Searching for Coal.-Ironstone accompanying Coal.-Precautions necessary in the Establishment of Iron Furnaces.-On Carbon as an original constituent part of the Globe.-On the Origin of Coal and its Deposition in Freshwater Basins or Lakes.-Experiments of Dr. MacCulloch on the Conversion of Vegetable Matter into Coal. On imperfect Coal Formations beyond the limits of the regular Coal Strata.-Hints to Landed Proprietors respecting the probability of finding Coal and Rock Salt in Districts where they are at present undiscovered.-Coal Mines in France, &c.-On the Consumption of Coal in England, and the period when it will be exhausted.

IT has been stated in the preceding chapter, that the upper conformable transition rocks are frequently associated with the lower series of secondary strata; so that from their position and mineral characters alone, no well marked line of division could be drawn between them there is however a truly remarkable difference in the nature of the organic remains in the transition rocks, and in the lower secondary strata. In the transition series, the organic remains are almost exclusively those of marine animals, which are believed to have lived in the deepest parts of the ocean. In the lower secondary