228 Murchison s Silurian System. 



Mr. Murchison concludes his observations on this coal 

 field by a notice of the faults and dislocations occasioned 

 by trap rocks. The district affords proofs of having been 

 raised up from beneath the surrounding new red sandstone 

 in separate wedge-shaped tracts, the most remarkable dis- 

 location being that which bounds the coal field to the east. 

 The coal measures along this line are not less than one thou- 

 sand feet thick, and as some of the lower seams of coal are 

 thrown up to the level of the overlying strata of new red sand- 

 stone, the upcast is thus shown to have exceeded one thousand 

 feet, though to what further extent has not yet been ascer- 

 tained. It will be recollected that we formerly explained 

 the elevated position of the Cherra coal measures in pre- 

 cisely the same way that Mr. Prestwich and Mr. Murchison 

 now account for the great upcast of the Coalbrook dale 

 field,* the only difference in the two cases being, that in 

 India the dislocation is not confined to the coal measures, 

 but extends to the old red sandstone, the whole series of 

 which, with the coal measures reposing on them, having 

 been at Cherra Ponji thrown 3000 feet above those which 

 have been recently found by Major Lister and others at 

 the bottom of the same mountains. It is of much im- 

 portance to draw comparisons between geological phenomena 

 of this nature in remote parts of the earth, as tending not 

 only to put our theories to the test, but also to correct 

 and give confidence to our views, which however compli- 

 cated they may appear when derived from a narrow field 

 of observation, become gradually simplified and important 

 in proportion as our data become general. 



The millstone grit, an important member of the coal mea- 

 sures being absent in the Coalbrook dale district, we shall 

 select Mr. Murchison' s description of it from other parts of 

 the work. 



In his description of the Knowlbury basin, Mr. Murchison 



* See Report of a Committee for investigating the Coal and Mineral resources 

 of India. Calcutta, 1838, pp. 24. 



