T. STEHRY HUNT. 47-( 1 7 I 



up in its course. The downward How of these waters, 

 progressively augmenting in temperature, continues un- 

 til it reaches depths determined by accidents of stratifi- 

 cation or by lines of fracture. Thence, in obedience to 

 hydrostatic laws, it rises again to the surface, sometimes 

 through porous beds, but more generally along the lines 

 of fracture, due to terrestrial movements. These fissures 

 are the veins, which become iu time incrusted and filled 

 up by deposits of mineral matter from the ascending 

 waters. The separation of these is due to the diminution 

 of the solvent power of the water as it cools in its up- 

 ward course and is moreover relieved of the pressure 

 which had augmented its capacity for solution. To this 

 we may often add the chemical effects of the influx at 

 various points into the channel of divers substances dis- 

 solved from other strata, bringing into play new affini- 

 ties in the original solution. 



The progressive incrustation and the final obliteration 

 of the channels as these become filled with veinstones 

 and the water ceases to flow, or else seek new channels, is 

 made apparent by the banded structure often seen in 

 these deposits, which frequently display bilateral sym- 

 metry in the arrangement of the successive layers, and 

 moreover often include in their centre geodes or imper- 

 fectly filled cavities, generally lined with crystals. In 

 this connection must not be forgotten the mechanical 

 force of crystallization from mineral solutions, which 

 like freezing water, often serves to open joints in the 

 rocks. The walls of veins sometimes show evidences 

 of this rending and disrupting force of crystallization. 



I have thus endeavored to place before you some of the 

 principles involved in the production of veinstones, and 

 to indicate to you how the terrestrial circulation, depend- 

 ent upon the rainfall and the ordinary laws which regu- 

 late the flow of liquids, suffices to dissolve from th< j solid 

 matter of the earth'scrust elements once widely diffused, 

 and to accumulate them by subsequent depositions in 

 the concretionary masses winch we call endogenous rocks 

 or veinstones. I cannot forbear to notice an analogy be- 

 tween the formation of these and the process by which a 

 vertebrate animal repairs a fracture in its osseous struc- 

 ture. In this case, the circulating Liquids bring to the 

 broken part the dissolved elements of bone, and there 



