218 Murchisoris Silurian System. 



prevalent belief of geologists when my researches commenced (1831), 

 that in all other parts of England, a great break existed between the 

 new red system and the coal measures, the phenomena of disruption 

 in the environs of Bristol, being assumed as the true types or patterns 

 of the general order. These upper coal measures of Shropshire are fur- 

 ther remarkable in bringing to light, for the first time in Great Britain, 

 a peculiar limestone interstratified with coal seams, and which from its 

 prevalent organic remains and mineral composition, I have referred to 

 fresh water origin. Though never exceeding eight or nine feet in thick- 

 ness, and sometimes dwindling away to two feet, this band is so re- 

 markably persistent, that when followed along all its sinuosities the 

 length of its course is about forty miles ; and even in a straight line 

 from Coedway, near the Breidden hills, to Tasley and Caughley, near 

 Bridgenorth, where it will presently be described, the distance is not 

 less than twenty-five miles ; and yet throughout such a space this little 

 stratum preserves the same structure, and contains the same micros- 

 copic shell, Microconchus carhonarius. The subsequent discovery by 

 which the limestone of Ardwick, near Manchester, was identified with 

 it, has given to this stratum a considerable additional importance, in 

 carrying out over so wide an area the evidences adduced in this volume 

 of the passage of the coal measures beneath the new red sandstone of 

 the central counties. Besides the zoological proofs of this limestone 

 having been formed in fresh water, I have already stated, that in mineral 

 characters it strongly resembles the lacustrine limestone of central 

 France, and I may now add, that the origin of the rocks in the two 

 countries is probably connected with similar causes. For as Auvergne 

 is a region which has been eminently subjected to volcanic action 

 during past ages, so its extensive formations of finely levigated lime- 

 stone are supposed to have been the produce of hot springs (the usual 

 attendants on volcanos), holding calcareous matter in solution, and de- 

 positing it amid the fine silt of ancient lakes ; in like manner the whole 

 of the surrounding region of Shropshire, in which limestone occurs, is 

 absolutely perforated by intrusive rocks of igneous origin, and hence 

 it is a fair deduction, that the peculiar limestone of this tract may like- 

 wise have been the result of volcanic hot springs. Other analogies will 

 strike those to whom the phenomena in central France are fa mili ar, 

 such as bituminous exudations and sources of mineral pitch which issue 

 from the surface at those points where eruptive rocks protrude ; but 

 these comparisons belong more properly to subsequent chapters. Diffi- 

 cult as it may be to reconstruct in imagination the condition of the 

 surface of this part of our island during the period of the coal formations, 

 the limestone and associated beds (whether formed exclusively in pure 



