NERBUDDA DISTRICT. 261 



relative directions of these lines on the sphere must be estimated with 

 reference to great circles of the sphere. The difficulty here consists in 

 not over-stretching the limits of probability in the estimation of the 

 modifying causes inseparable from such calculations, for the sake of a 

 symmetrical result ; a difficulty which cannot fail to strike any one who 

 has carefully studied M. de Beaumont's great work. 



But after making an estimate, or obtaining from a general estimation of 

 the facts, a knowledge of the direction of our range-lines sufficiently 

 exact to warrant the application of those mathematical calculations, 

 to which we must have recourse in investigating the parallelism of lines 

 far apart on the sphere ; and after having found a parallel for our 

 Asiatic range-lines among the European systems adopted as our standard, 

 the next difficulty is found in the rarity of examples in which the lines 

 thus fixed for the directions of ranges, so definitely coincide with geologi- 

 cal boundaries, or are in other ways so clearly connected with geological 

 facts as to furnish us with data for arriving at a really satisfactory 

 determination of these geological ages. It is self-evident that however 

 clearly determinable the direction of the ranges, or however certainly 

 attributable to great fissure or fault lines they may be, still if they be not 

 very definitely connected with the boundaries between other disturbances 

 of rocks, demonstrably distinct in age, little or nothing can safely be con- 

 cluded as to their own relative position in geological chronology (a). 



Difficulties such as these, in the application of this theory, have been 

 strongly insisted upon, and been by some considered, we believe, as 

 sufficient ground, for its rejection ; but, as before stated, the district with 

 which we have to do furnishes us with conditions very favorable for 

 its application here. The line of the range (a matter often so difficult 

 to determine) is here traced unmistakeably and definitely. 



(a) As a case in point we may refer to Sir C. Lyell's Analysis of M. de Beaumont's 

 views concerning the age of the elevation of the main chain of the Pyrenees. Principles 

 of Geology, IXth. Edition, 1853, p. 163. 



