47 



plicable. If they are made in some cases, where 

 they really can be made with great ease and pre- 

 cision, that, in some other place, is found impos- 

 sible ; and nothing is gained by adopting an order 

 in one part which cannot be extended to the 

 whole. Whoever may make the attempt will soon 

 be convinced that he has undertaken an imprac- 

 ticable task ; and that he cannot even approach 

 the accomplishment of his wishes, without sacri- 

 ficing utility and convenience to an imaginary 

 regularity. 



Every rock which is described, is therefore 

 considered a variety, no other term being equally 

 unexceptionable ; and as it must be considered a 

 variety, in a geological sense only, it cannot well 

 mislead a reader. The most important of these 

 are generally placed first in that division in which 

 they may occur ; or, when necessary, additional 

 remarks are subjoined, by which the student may 

 judge of the comparative importance of the diffe- 

 rent varieties. That, perhaps, is of little mo- 

 ment. As the object of the arrangement is geo- 

 logical, he will not be long in discovering the re- 

 lative value and constancy of the rocks which he 



