Outlines of Geology. 37 



sited before many of those unevennesses which give' rise to our 

 present hills and dales were carved out upon the surface, and often 

 where even a deep and extensive valley intervenes, the same strata 

 running in the same direction, and at the same levels, are found 

 continuous on both its sides ; except in some particular cases, where 

 the valley is very narrow and abrupt, and its sides perpendicular, 

 and where it appears to have been formed by the dislocation and 

 fracture of the ground, once continuous, in which it occurs. 

 . In consequence of the peculiar arrangement of the coal strata, 

 a section of them often gives the idea of a basin, or boat-shaped 

 concavity, which has been successively filled with the various 

 substances that occur in it ; the seams of coal vary in number and 

 in thickness, as well as in quality, and the upper seams are ge- 

 nerally imperfect. 



In consequence of the dip of the strata, it not unfrequently hap- 

 pens that we have an opportunity of examining and ascertaining 

 the nature of the lowest seams, which, though deep and out of 

 reach in one part of the coal-field, are superficial at another. 

 This is shown at Cross-fell, where the crow-coal rises to-day, 

 which, in consequence of the inclination of the beds, is considered 

 to be nearly 460 fathoms below the lowest of the Newcastle beds, 

 a little to the east of that town. 



The description of one coal formation applies, in general, to 

 others ; but there are certain circumstances which give peculi- 

 arities to some of our coal districts, among which the iron- works 

 are deserving attention. The ore which is here worked is the 

 clay iron-stone ; an ore poor in itself, but deriving value from the 

 abundance of coal that attends it. 



Some writers have amused themselves with speculations re- 

 specting the exhaustion of our coal-mines, and have calculated 

 the number of years, or centuries, that the stock on hand is likely 

 to last. When, indeed, we reflect upon the vast importance of 

 this specie3 of fuel in a country dependent not merely for its pros- 

 perity, but even for its very existence, upon its manufactures and 

 consequent commerce ; when we remember its enormous and in- 

 creasing consumption ; when we consider that the metropolis only 



