104 DISPOSITION'S, FRACTURES AND 



of the motions of these. The very existence of some 

 veins is further involved in that of fractures, and it is 

 therefore an unavoidable object of consideration in this 

 place. 



The fractured ends of a stratum, or rock, may 

 remain in contact, without any intervening material, 

 or they may be separated to a distance in the same 

 manner. But this is a rare occurrence, and is only 

 observed in the more recent fractures and displace- 

 ments ; generally, indeed, in those in which we can 

 almost name the period of fracture. It is a general 

 rule, on the contrary, that some substance intervenes 

 where the separation occurs ; and this, according to 

 its quality and thickness, forms veins of different 

 characters and dimensions. It is equally obvious, 

 that intersecting veins will be the natural consequence 

 of fractures and slides occurring at different periods of 

 time- 

 In the minuter appearances, the matter of the veins 

 is generally quartz or carbonat of lime, sometimes in- 

 durated clay : in the larger, conglomerated substances, 

 or portions of the unstratified rocks occur ; but 

 enough has already been said on a subject which 

 nevertheless required to be noticed among those phe- 

 nomena with which it is so intimately connected. I 

 need only here remark, that although the reunion of 

 fractured rocks is generally produced by the interven- 

 tion of those substances which form the minuter veins, 

 and generally, it is probable, from watery infiltrations 

 of silica or carbonat of lime, the process, in some 

 cases, appears rather more mysterious. Thus I have 

 observed, that hornblende schist is reunited by veins 

 of the same substance, and gneiss by intermediate 

 laminae of granite. A little examination is however 

 sufficient to show the real nature of these ; the new 



