CHAPTER VI.

CARBONIFEROUS SYSTEM.

Introduction—Upper Coal Measures and Freshwater Limestone.

Introduction.

My chief object in this and the next six chapters, is to convey a clear idea of the prominent relations of the carboniferous strata to the overlying and underlying systems,and to furnish means of comparing these rocks in the region under examination withthose of similar age in other parts of Great Britain. Following up the inquiry com-menced towards the end of the fourth chapter, I would first direct attention to thosetracts, where there are evidences of a passage downwards from the Lower New RedSandstone into the carboniferous strata. It will afterwards he shown, that the under-lying formations of millstone grit and carboniferous or mountain limestone, are unpro-ductive of coal; and lastly it will appear, that the carboniferous limestone graduatesdownwards into the Old Red Sandstone with as much regularity as the Lower NewRed Sandstone passes down into the upper coal measures. These general views areexplained in this wood-cut.

10.

a. Lower New Red Sandstone, with calcareous concretions described in the last chapter.

b. Upper coal measures with freshwater limestone.

c. Main coal.

d. Lower coal and ironstone.

e. Millstone grit.

f. and g. Carboniferous limestone and shale.

h. Conglomerate and sandstone, or upper formation of the Old Red System.

The various coal-fields will be described in the following order.

1. Shrewsbury. The carboniferous strata around Shrewsbury will be shown to con-sist of a younger or upper zone, which immediately succeeding to the Lower New RedSandstone, contains within it a limestone of freshwater or estuary origin, peculiar tothe coal-fields of the central counties of England.

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