134 Physical Geography. 



the limestone is about 2,500 feet thick. Going north 

 to Haverfordwest it rapidly thins out, and finally dis- 

 appears by overlap in a distance of twelve miles. A 

 rapid thinning of the same strata also takes place 

 between the shore of Bristol channel in Glamorganshire 

 and the north side of the South Wales coal-field. In 

 the Mendip Hills the limestone has also a thickness of 

 about 2,500 feet. Traces of it are still seen south 

 of Bideford Bay, at Cannington Park, a few miles north- 

 west of Bridgewater, while on the northern borders of 

 the Culm-measures of North Devon, it may be said to 

 have almost entirely disappeared as a special formation. 

 Among the limestone hills of Derbyshire it is of enor- 

 mous thickness, and its base is unknown ; but s in- 

 distinct is the bedding in part of the centre of that 

 region, that it is often as hard to make out the 

 details of stratification as it is in a large consolidated 

 modern coral reef. North of Clitheroe the bosses of 

 limestone are in places remarkably massive, and thin 

 away in various directions so rapidly, that the incautious 

 geologist is at first tempted to imagine faults where 

 none exist. Further north, near Settle, Kendal, and 

 round the sides of the Yale of Eden, it is well developed 

 and distinctly bedded ; but passing east and north, into 

 Durham and Northumberland, it rapidly splits up into 

 a few comparatively insignificant bands, separated by 

 thick interstratifications of shale, sandstone, and minor 

 beds of coal. The lower coal-fields in Scotland lie in 

 equivalent strata. 



In Ireland the phenomena are still more remarkable, 

 for in the south and south-west, as described by Jukes, 

 the same masses of limestone in a few miles sometimes 

 thin away from some 2,000 to 200 or 300 feet in 

 thickness. 





