176 J. Barrell — Relations of Subjacent Igneous 



as the lit-par-lit structure. (For further discussion, see 

 Part III.) 



Prevention of Deep Penetration of Meteoric Waters. 



In the discussion of the anamorphism of the rocks of 

 northwestern Connecticut, it developed that there is evi- 

 dence, in the addition of tourmaline and silicates, that 

 rising waters were active, but no conclusive evidence has 

 been presented that the waters were of magmatic origin. 

 The relative place which meteoric and magmatic waters 

 hold in carrying forward the work of metamorphism is a 

 long debated question. In contact metamorphism, it is 

 now held by the majority of workers that magmatic 

 waters are the controlling factor, but meteoric waters of 

 vadose or connate origin are still commonly regarded as 

 the agents active in regional metamorphism. 



It was formerly an accepted part of geologic theory 

 that the mechanism of volcanoes involved a free down- 

 ward percolation of sea waters. The Daubree experi- 

 ment, showing the capillary passage of water through a 

 porous sandstone against pressure and into a steam- 

 filled chamber, was thought to support the view. The 

 diffusion of water under great pressure through the 

 intermolecular pores of glass and metals has also been 

 held to be supporting evidence. 



The conditions of the Daubree experiment do not 

 apply, however, to the vast thickness of non-porous 

 crystalline rocks. The diffusion of water through glass 

 and metals is effective only under an enormously steep 

 pressure-gradient which has no direct relation to the high 

 pressures but low pressure-gradient of the earth ^s 

 interior. Igneous rocks come from depths below the 

 zone of sedimentary rocks and the emanations show com- 

 positional characters in the possession of abundant 

 carbon gases, fluorine, and boron, which indicate a lack 

 of relationship to downward percolations. Lastly, and 

 perhaps most conclusively, mining operations show the 

 zone of meteoric waters to be relatively shallow, confined 

 in definite zones to porous or fissured rocks, and the rocks 

 below to be dry. Soluble constituents such as salt and 

 gypsum, if in rocks well below base-level, are permanently 

 preserved from solution and show the absence of per- 

 vasive circulating waters. 



These reasons have caused the majority of geologists 

 to look upon gases or fluids which carry forward the 



