on " Researches m Physical Geology." 1 75 



locations. In my investigations it is unnecessary to suppose 

 any but the lowest degree of solidification in the elevated 

 mass ; and therefore it is manifestly quite inadmissible to 

 assume that it could not be dislocated by an elevatory force 

 before its jointed structure had become sufficiently developed 

 to determine the directions of dislocation. Yet the only force 

 which can possibly attach to the objection above quoted de- 

 pends entirely on this assumption, which, in fact, involves the 

 very point at issue, viz. whether the jointed structui'e of dis- 

 turbed masses has been in great measure superinduced j^re- 

 viotisly or subseque7itly to their elevation. It is not, however, 

 by this kind of a p7-iori reasoning, founded on what we are 

 altogether ignorant of, that the merits of geological theories 

 can be determined; and to attempt to do so is to depart from 

 those principles of inductive philosophy which alone have 

 enabled man to comprehend with clearness and precision so 

 much that is beautiful and wonderful in the laws of nature. 

 I have elsewhere stated that I have not entered into these dis- 

 cussions in the spirit of advocacy of preconceived opinions; and 

 with respect to the two theories, of which one would assign 

 the directions of dislocation principally to the manner in which 

 the elevating force has acted, and the other to the previously 

 jointed state of the mass, I have endeavoured to act with 

 perfect impartiality. I have indicated how their relative 

 claims may probably be decided by observation, by which alone, 

 I assert, these claims can be determined, and not by the kind 

 of reasoning on which both the objections above noticed are 

 founded. 



With a view to this determination I have lately made some 

 careful observations in the limestone and gritstone district of 

 Derbyshire. In a particular and thick mass of limestone 

 which pervades the greater })art of that mining district, the 

 joints are remarkably well developed. They form two systems 

 at right angles (or very nearly so) to each other, which pre- 

 serve their directions with remarkable accuracy in every part 

 of the district. The other beds also have their principal joints 

 in the same directions wherever they can be distinctly re- 

 cognised ; and such also is the case with the immense mass 

 of gritstone superincumbent on the shale and limestone. One 

 of these directions is a little west of the magnetic north ; the 

 other being consequently a little north of magnetic east, while 

 the directions of all the characteristic dislocations of the district 

 are nearly east and west and north and south, thus deviating 

 from those of the joints by an angle of from 20° to 30°, pre- 

 cisely of that magnitude which is too large to be possibly at- 

 tributed to any error of observation, and too small to admit 



